Add admin identity module: better-auth, per-app permissions, invitations (#12)

Reviewed-on: #12
Co-authored-by: Patrick Müller <mail@pmueller.me>
Co-committed-by: Patrick Müller <mail@pmueller.me>

src/models/admin/Admin.db.ts

@@ -0,0 +1,55 @@
+import * as dotenv from 'dotenv';
+import mysql from 'mysql2';
+import {Kysely, MysqlDialect} from 'kysely';
+import {AdminDatabase} from './admin.schema.js';
+import logger from '../../middleware/logger.js';
+
+dotenv.config();
+
+/**
+ * The admin module is the one place in this API that does not use the
+ * `mariadb` driver: better-auth talks to the database through Kysely, whose
+ * MySQL dialect expects a mysql2 pool. The other domains keep their own
+ * `mariadb` pools (see Feedback.db.ts) - this is an addition, not a migration.
+ *
+ * The pool is the callback-style `mysql2` one, NOT `mysql2/promise`: Kysely's
+ * MysqlDialect calls `pool.getConnection((err, conn) => ...)`. The promise
+ * wrapper ignores that callback and returns a Promise instead, so every query
+ * through Kysely would hang forever with no error - which is exactly what it
+ * did until the integration tests caught it.
+ *
+ * timezone 'Z' matters: better-auth computes session and token expiry in UTC.
+ * Without it mysql2 would write and read those DATETIMEs in the process's local
+ * zone, so sessions would expire an hour early or late depending on DST.
+ */
+
+export namespace NachklangAdminDB {
+	export const pool = mysql.createPool({
+		host: process.env.DB_HOST,
+		user: process.env.DB_USER,
+		password: process.env.DB_PASSWORD,
+		database: process.env.ADMIN_DB,
+		// The other modules' pools default to 3306. This one is configurable so
+		// the integration tests can point at a throwaway container on another
+		// port without touching a developer's real .env.
+		port: parseInt(process.env.DB_PORT || '3306', 10),
+		connectionLimit: 5,
+		timezone: 'Z'
+	});
+
+	// mysql2 emits connection trouble as an event on the pool, not only as a
+	// rejected query. Without a listener Node turns that into an
+	// uncaughtException, so a database restart would take the whole API - and
+	// with it the calendar, feedback and tickets domains - down with it.
+	// Individual queries still reject, and their callers still answer 500.
+	pool.on('error', (err: unknown) => {
+		logger.error('Admin database pool error', {detail: (err as any)?.message});
+	});
+
+	// Handed to better-auth as `database: {dialect, type: 'mysql'}`.
+	export const dialect = new MysqlDialect({pool});
+
+	// Used by this module's own services for the two custom tables and for
+	// permission lookups that join better-auth's `user`.
+	export const db = new Kysely<AdminDatabase>({dialect});
+}

src/models/admin/Admin.router.ts

@@ -0,0 +1,48 @@
+import express, {Request, Response} from 'express';
+import {requireAppAccess, requireSignedIn} from './admin.middleware.js';
+import {usersAdminRouter} from './users/users.admin.router.js';
+import {invitationsRouter} from './invitations/invitations.router.js';
+
+/**
+ * The admin module's JSON routes. Deliberately *not* the better-auth handler:
+ * that one is mounted separately in app.ts, ahead of express.json(), because it
+ * needs the raw request body stream.
+ *
+ * Mounted at /admin, so the tree is:
+ *   /admin/me            any signed-in account
+ *   /admin/users/*       admin permission
+ *   /admin/invitations/* admin permission
+ */
+export const adminRouter = express.Router();
+
+/**
+ * @swagger
+ * /admin/me:
+ *      get:
+ *          summary: The current user's identity and app permissions
+ *          description: Used by every frontend to decide what to show. The API remains the real gate.
+ *          tags: [admin]
+ *          responses:
+ *              200:
+ *                  description: Success
+ *              401:
+ *                  description: Not signed in
+ *              403:
+ *                  description: Account disabled
+ */
+adminRouter.get('/me', requireSignedIn, (req: Request, res: Response) => {
+	res.status(200).send({
+		id: res.locals.admin.id,
+		email: res.locals.admin.email,
+		fullName: res.locals.admin.displayName,
+		// `permissions` is the full (app, role) truth; `apps` is the distinct
+		// apps within it. Both are sent because the three frontends only ever ask
+		// "may I show this app?", and keeping `apps` means a finer permission can
+		// land here without a coordinated deploy of all of them.
+		permissions: res.locals.admin.permissions,
+		apps: res.locals.admin.apps
+	});
+});
+
+adminRouter.use('/users', requireAppAccess('admin'), usersAdminRouter);
+adminRouter.use('/invitations', requireAppAccess('admin'), invitationsRouter);

src/models/admin/admin.auth.ts

@@ -0,0 +1,162 @@
+import {betterAuth} from 'better-auth';
+import {APIError} from 'better-auth/api';
+import {passkey, getAuthenticatorName} from '@better-auth/passkey';
+import {NachklangAdminDB} from './Admin.db.js';
+import {invitationsPlugin} from './invitations/invitations.plugin.js';
+import {sendPasswordResetMail} from './admin.mail.js';
+import * as UsersService from './users/users.admin.service.js';
+import logger from '../../middleware/logger.js';
+import {
+	ADMIN_ALLOWED_ORIGINS,
+	API_BASE_URL,
+	BETTER_AUTH_SECRET,
+	CLIENT_IP_HEADERS,
+	PASSKEY_RP_ID,
+	TRUSTED_PROXY_IPS,
+	isProd
+} from './admin.config.js';
+
+/**
+ * The single better-auth instance for all *.nachklang.art apps. Mounted in
+ * app.ts at /admin/auth/* with better-auth's own node handler, ahead of
+ * express.json() (it needs the raw body stream).
+ *
+ * The session cookie is what every app trusts. Everything else in this module -
+ * permissions, invitations, the admin UI - hangs off it.
+ */
+
+const DAY = 60 * 60 * 24;
+
+// Dev runs the apps on plain localhost ports; cookies ignore the port, so
+// single-sign-on across them works without fake subdomains or mkcert.
+const localhostOrigins = [
+	'http://localhost:3000',
+	'http://localhost:3001',
+	'http://localhost:3002',
+	'http://localhost:3003'
+];
+
+const trustedOrigins = isProd
+	? ADMIN_ALLOWED_ORIGINS
+	: Array.from(new Set([...ADMIN_ALLOWED_ORIGINS, ...localhostOrigins]));
+
+export const auth = betterAuth({
+	appName: 'Nachklang',
+	database: {
+		dialect: NachklangAdminDB.dialect,
+		type: 'mysql'
+	},
+	basePath: '/admin/auth',
+	// Mandatory once crossSubDomainCookies is on: better-auth derives the
+	// cookie domain and its own absolute URLs from this.
+	baseURL: API_BASE_URL,
+	secret: BETTER_AUTH_SECRET,
+	trustedOrigins,
+
+	emailAndPassword: {
+		enabled: true,
+		// There is no public sign-up: accounts exist only through an
+		// invitation (see invitations.plugin.ts). This also makes
+		// auth.api.signUpEmail throw, which is intended.
+		disableSignUp: true,
+		sendResetPassword: async ({user, url}) => {
+			await sendPasswordResetMail(user.email, user.name, url);
+		}
+	},
+
+	user: {
+		additionalFields: {
+			// Not `returned`, and not settable through the API: disabling is an
+			// admin action on /admin/users/:id/disable, never something a
+			// session owner can flip on themselves.
+			disabled: {
+				type: 'boolean',
+				defaultValue: false,
+				input: false,
+				returned: false
+			}
+		}
+	},
+
+	session: {
+		expiresIn: 30 * DAY,
+		updateAge: DAY
+		// Deliberately no cookieCache: requireAppAccess hits the database on
+		// every request anyway, and a cached session would keep a disabled
+		// user or a revoked session alive for the cache's lifetime.
+	},
+
+	advanced: {
+		// Fixes the cookie name across releases so the frontends' middleware can
+		// check for it: "nachklang.session_token", or
+		// "__Secure-nachklang.session_token" over https.
+		cookiePrefix: 'nachklang',
+		crossSubDomainCookies: isProd
+			? {enabled: true, domain: '.nachklang.art'}
+			: {enabled: false},
+		ipAddress: {
+			// better-auth reads the request itself and does not know about
+			// Express's `trust proxy`, so both the header and the trusted hops
+			// have to be named here. Getting this wrong does not fail loudly -
+			// it collapses every client into one rate-limit bucket. See the
+			// commentary on CLIENT_IP_HEADERS in admin.config.ts.
+			ipAddressHeaders: CLIENT_IP_HEADERS,
+			...(TRUSTED_PROXY_IPS.length > 0 ? {trustedProxies: TRUSTED_PROXY_IPS} : {})
+		}
+	},
+
+	rateLimit: {
+		enabled: true,
+		// Passenger may run more than one instance; an in-memory limiter would
+		// then give each of them its own budget.
+		storage: 'database'
+	},
+
+	plugins: [
+		passkey({
+			rpID: PASSKEY_RP_ID,
+			rpName: 'Nachklang',
+			origin: ADMIN_ALLOWED_ORIGINS,
+
+			registration: {
+				// Without this, every passkey is stored with name = NULL and the
+				// account page can only label them all "Passkey" - useless at the
+				// one moment that list matters, when someone has to remove the
+				// passkey on the device they just lost.
+				//
+				// The AAGUID identifies the authenticator *model* (not a device
+				// and not a person), and better-auth ships the lookup table, so
+				// this yields "1Password", "iCloud Keychain", "Windows Hello".
+				// It only fills a blank: a name the client sent always wins, and
+				// an unknown AAGUID leaves the column NULL as before.
+				afterVerification: async ({verification}) => {
+					const name = getAuthenticatorName(verification.registrationInfo?.aaguid);
+					return name ? {name} : undefined;
+				}
+			}
+		}),
+		invitationsPlugin()
+	],
+
+	databaseHooks: {
+		session: {
+			create: {
+				before: async session => {
+					const access = await UsersService.loadAccess(session.userId);
+					if (access?.disabled) {
+						logger.warn('Admin: sign-in attempt by a disabled account', {userId: session.userId});
+						// Throwing rather than returning false: `false` aborts
+						// the session write silently and the caller sees a
+						// confusing success-shaped response with no cookie.
+						throw new APIError('FORBIDDEN', {
+							code: 'ACCOUNT_DISABLED',
+							message: 'Dieses Konto ist deaktiviert.'
+						});
+					}
+				}
+			}
+		}
+	}
+});
+
+export type AdminAuth = typeof auth;

src/models/admin/admin.bootstrap.ts

@@ -0,0 +1,68 @@
+import * as UsersService from './users/users.admin.service.js';
+import * as InvitationsService from './invitations/invitations.service.js';
+import {sendInvitationMail} from './admin.mail.js';
+import {ACCESS_ROLE} from './admin.schema.js';
+import {ADMIN_APP_URL, ADMIN_BOOTSTRAP_EMAIL, LOG_INVITE_LINKS} from './admin.config.js';
+import logger from '../../middleware/logger.js';
+
+/**
+ * Solves the empty-database problem: with invite-only accounts and no public
+ * sign-up, a fresh nachklang_admin has nobody who can invite anybody. Rather
+ * than a CLI script somebody has to remember to run against production, the API
+ * makes sure on every start that ADMIN_BOOTSTRAP_EMAIL can get in.
+ *
+ * Idempotent by design - it is safe on every restart:
+ *   - an active admin already exists  -> do nothing
+ *   - the address exists as a user    -> grant it `admin`
+ *   - an open invitation exists       -> do nothing (do not re-mail on restart)
+ *   - otherwise                       -> invite, and mail the link
+ *
+ * Never throws: a database blip at boot must not stop the API from serving the
+ * calendar, feedback and tickets domains.
+ */
+export const bootstrapAdmin = async (): Promise<void> => {
+	try {
+		if (!ADMIN_BOOTSTRAP_EMAIL) {
+			return;
+		}
+
+		const email = ADMIN_BOOTSTRAP_EMAIL.trim().toLowerCase();
+
+		if ((await UsersService.countActiveAdmins()) > 0) {
+			return;
+		}
+
+		const existing = await UsersService.findUserByEmail(email);
+		if (existing) {
+			await UsersService.grantPermission(existing.id, 'admin', null);
+			logger.info('Admin bootstrap: granted the admin permission to the existing bootstrap user', {email});
+			return;
+		}
+
+		// An expired invitation is not "open", so the next restart re-issues
+		// one - which is the recovery path if the first mail never arrived.
+		if (await InvitationsService.hasOpenInvitationFor(email)) {
+			logger.info('Admin bootstrap: an open invitation already exists', {email});
+			return;
+		}
+
+		const invitation = await InvitationsService.createInvitation(
+			email,
+			'Nachklang Admin',
+			[{app: 'admin', role: ACCESS_ROLE}],
+			null
+		);
+
+		const mailed = await sendInvitationMail(email, 'Nachklang Admin', invitation.token, invitation.expiresAt);
+		logger.info('Admin bootstrap: invitation created', {email, mailed});
+
+		// With the mail relay off, the logged link is how a local setup gets its
+		// first admin. Explicit opt-in (see LOG_INVITE_LINKS): the link is a
+		// live credential, so this must never depend on NODE_ENV alone.
+		if (LOG_INVITE_LINKS) {
+			logger.info(`Admin bootstrap: ${ADMIN_APP_URL}/accept-invite?token=${invitation.token}`);
+		}
+	} catch (e: any) {
+		logger.error('Admin bootstrap failed', {detail: e?.message});
+	}
+};

src/models/admin/admin.config.ts

@@ -0,0 +1,170 @@
+import * as crypto from 'crypto';
+import * as dotenv from 'dotenv';
+import logger from '../../middleware/logger.js';
+
+dotenv.config();
+
+/**
+ * One place that reads the admin module's environment. Both admin.auth.ts
+ * (better-auth trustedOrigins, passkey origins) and app.ts (CORS) need the
+ * same origin list, and a second parser would drift from this one.
+ *
+ * Read this before changing the environment handling below: several security
+ * properties depend on it, and they are deliberately arranged to fail *safe*.
+ *
+ * `NODE_ENV` is opt-in to relaxed behaviour, not opt-in to strict behaviour.
+ * Only the explicit values 'development' and 'test' relax anything; anything
+ * else - including NODE_ENV being unset, which is exactly what a fresh Plesk
+ * vhost gives you - is treated as production. The inverse arrangement is a
+ * trap: it degrades the cookie domain, the CORS origin list and the signing
+ * key all at once, and every one of those failures is silent.
+ *
+ * The signing key is never allowed to be a known constant. In dev, an unset
+ * BETTER_AUTH_SECRET becomes a random per-process value: sessions do not
+ * survive a restart, which is mildly annoying and much better than a default
+ * secret that can be copied out of this file and used against production.
+ */
+
+const nodeEnv = process.env.NODE_ENV;
+
+// Explicitly relaxed environments. Everything else, unset included, is strict.
+const isRelaxedEnv = nodeEnv === 'development' || nodeEnv === 'test';
+
+export const isProd = !isRelaxedEnv;
+
+const required = (name: string, devDefault: string): string => {
+	const value = process.env[name];
+	if (value) {
+		return value;
+	}
+	if (isProd) {
+		logger.error(
+			`Admin module: ${name} is not set (NODE_ENV=${nodeEnv ?? 'unset'}, so strict mode applies; ` +
+			'set NODE_ENV=development for local work)'
+		);
+		throw new Error(`${name} must be set unless NODE_ENV is development or test`);
+	}
+	return devDefault;
+};
+
+export const API_BASE_URL = required('API_BASE_URL', 'http://localhost:3000');
+export const ADMIN_APP_URL = required('ADMIN_APP_URL', 'http://localhost:3002');
+
+// 32+ random bytes; better-auth signs cookies and reset tokens with it.
+// Rotating it invalidates every session, which is why it is not derived.
+// There is no hardcoded fallback on purpose: a constant committed here would
+// be a published signing key the moment someone deploys without setting it.
+export const BETTER_AUTH_SECRET = required(
+	'BETTER_AUTH_SECRET',
+	crypto.randomBytes(48).toString('base64')
+);
+
+// Passkeys are bound to this: a credential registered for "nachklang.art"
+// works on every *.nachklang.art host, one registered for "localhost" only
+// works in dev. Changing it invalidates every registered passkey.
+export const PASSKEY_RP_ID = process.env.PASSKEY_RP_ID || (isProd ? 'nachklang.art' : 'localhost');
+
+const parseList = (value: string | undefined, fallback: string[]): string[] => {
+	const parsed = (value || '')
+		.split(',')
+		.map(entry => entry.trim())
+		.filter(entry => entry.length > 0);
+
+	return parsed.length > 0 ? parsed : fallback;
+};
+
+// The apps whose frontends may talk to /admin/* with credentials.
+export const APP_ORIGINS = parseList(process.env.APP_ORIGINS, []).map(origin => origin.replace(/\/$/, ''));
+
+// Kept in sync by construction rather than by three separate lists: the admin
+// app itself always counts, and dev adds the local ports.
+export const ADMIN_ALLOWED_ORIGINS = Array.from(new Set([
+	ADMIN_APP_URL.replace(/\/$/, ''),
+	...APP_ORIGINS
+]));
+
+/**
+ * The header the reverse proxy puts the real client IP in, and the proxy hops
+ * to trust when reading it.
+ *
+ * This matters more than it looks. better-auth does not know about Express's
+ * `trust proxy`; it reads the request itself. If it cannot resolve a client IP
+ * it falls back to a single shared bucket ("no-trusted-ip") for the whole
+ * process - and /sign-in/* carries a default of 3 requests per 10 seconds, so
+ * one noisy client would lock every user out of every app.
+ *
+ * Without TRUSTED_PROXY_IPS, better-auth rejects a multi-value
+ * x-forwarded-for outright (it cannot tell which hop is the client), which is
+ * exactly the case that produces that shared bucket. Set it to the address or
+ * CIDR of Plesk's nginx. Conversely, listing a header the proxy does not
+ * overwrite lets a client set its own IP and mint itself an unlimited
+ * brute-force budget - so the default is the single header nginx sets, not a
+ * permissive list.
+ */
+
+/**
+ * `CLIENT_IP_HEADERS=none` trusts no header at all.
+ *
+ * This is the escape hatch for the one case where the wrong setting is worse
+ * than no setting: if the proxy turns out NOT to overwrite the header we are
+ * trusting, any client can send it and mint itself an unlimited brute-force
+ * budget against /sign-in. Falling back to the shared bucket is bad (one noisy
+ * client can lock the organisation out for ten seconds at a time) but it is
+ * bad in a way that fails closed, and it can be reverted from the environment
+ * without a deploy.
+ *
+ * Reach for it only after a check has actually failed - `SELECT ipAddress FROM
+ * session ORDER BY createdAt DESC` showing 127.0.0.1 or NULL for a real remote
+ * sign-in - and take it back out once the header is configured.
+ *
+ * An empty or unset value still means "use the default", not "trust nothing":
+ * a stray blank line in a .env must not silently change how requests are
+ * bucketed. Only the explicit word does that.
+ */
+const TRUST_NO_HEADER = 'none';
+
+export const TRUST_NO_CLIENT_IP_HEADER =
+	(process.env.CLIENT_IP_HEADERS || '').trim().toLowerCase() === TRUST_NO_HEADER;
+
+// An empty array is what better-auth reads as "no headers": it only falls back
+// to its own default when the option is absent, and `[]` is truthy.
+export const CLIENT_IP_HEADERS = TRUST_NO_CLIENT_IP_HEADER
+	? []
+	: parseList(process.env.CLIENT_IP_HEADERS, ['x-real-ip']);
+
+export const TRUSTED_PROXY_IPS = parseList(process.env.TRUSTED_PROXY_IPS, []);
+
+if (isProd && TRUST_NO_CLIENT_IP_HEADER) {
+	logger.warn(
+		'Admin module: CLIENT_IP_HEADERS=none - no client-IP header is trusted, so every ' +
+		'request shares one rate-limit bucket and /sign-in allows 3 attempts per 10 seconds ' +
+		'for everyone combined. This is the safe fallback, not a destination: configure the ' +
+		'header the proxy actually sets and remove it.'
+	);
+} else if (isProd && TRUSTED_PROXY_IPS.length === 0) {
+	logger.warn(
+		'Admin module: TRUSTED_PROXY_IPS is not set. If the proxy sends a multi-value ' +
+		`${CLIENT_IP_HEADERS.join('/')}, better-auth cannot resolve a client IP and every ` +
+		'request shares one rate-limit bucket. Verify with: SELECT `key` FROM rateLimit - ' +
+		'a "no-trusted-ip" row means this is happening. A single-value header needs no ' +
+		'trusted proxies, so this warning is expected on a plain single-proxy setup.'
+	);
+}
+
+export const ADMIN_BOOTSTRAP_EMAIL = process.env.ADMIN_BOOTSTRAP_EMAIL || '';
+
+/**
+ * Whether to write invitation links to the log. An invitation link is a live
+ * account-creation credential, so this is an explicit opt-in rather than
+ * something inferred from NODE_ENV: local work needs it (the mail relay is
+ * usually off, and only the token's hash is stored, so there is otherwise no
+ * way to walk the accept flow), and production must never have it.
+ *
+ * Refused outright in strict mode, so setting it in a production .env by
+ * accident fails at boot instead of quietly filling the log with credentials.
+ */
+export const LOG_INVITE_LINKS = process.env.ADMIN_LOG_INVITE_LINKS === 'true' && !isProd;
+
+if (process.env.ADMIN_LOG_INVITE_LINKS === 'true' && isProd) {
+	logger.error('Admin module: ADMIN_LOG_INVITE_LINKS is set outside development - refusing to log invitation tokens');
+}

src/models/admin/admin.errors.ts

@@ -0,0 +1,17 @@
+import {Response} from 'express';
+import {Guid} from 'guid-typescript';
+import logger from '../../middleware/logger.js';
+
+/**
+ * Same catch-block convention as the feedback and tickets modules: log with a
+ * reference guid, never hand the real error message to the client.
+ */
+export const sendServerError = (res: Response, e: any): void => {
+	const errorGuid = Guid.create().toString();
+	logger.error('Error handling a request: ' + e.message, {reference: errorGuid});
+	res.status(500).send({
+		status: 'PROCESSING_ERROR',
+		message: 'Internal Server Error. Try again later.',
+		reference: errorGuid
+	});
+};

src/models/admin/admin.interface.ts

@@ -0,0 +1,120 @@
+/**
+ * Swagger component definitions for the admin module. Picked up by
+ * swagger-jsdoc through the `src/models/**\/*.interface.ts` glob in
+ * app.factory.ts.
+ *
+ * Note what is *not* documented here: the better-auth routes under
+ * /admin/auth/* (sign-in, sign-out, reset-password, passkey ceremonies, and
+ * the invitation preview/accept endpoints). better-auth owns those paths and
+ * their shapes; duplicating them by hand would only drift on the next upgrade.
+ */
+
+/**
+ * @swagger
+ * components:
+ *   securitySchemes:
+ *     AdminSessionCookie:
+ *       type: apiKey
+ *       in: cookie
+ *       name: nachklang.session_token
+ *       description: >
+ *         Set by /admin/auth/sign-in/email. Over https the name is
+ *         __Secure-nachklang.session_token and the cookie is scoped to
+ *         .nachklang.art, so one sign-in covers every *.nachklang.art app.
+ *   schemas:
+ *     AdminApp:
+ *       type: string
+ *       enum: [calendar, feedback, tickets, admin]
+ *       description: Holding "admin" is what allows managing users and invitations.
+ *     AdminMe:
+ *       type: object
+ *       properties:
+ *         id:
+ *           type: string
+ *         email:
+ *           type: string
+ *         fullName:
+ *           type: string
+ *         apps:
+ *           type: array
+ *           items:
+ *             $ref: '#/components/schemas/AdminApp'
+ *     AdminUserSession:
+ *       type: object
+ *       properties:
+ *         id:
+ *           type: string
+ *         createdAt:
+ *           type: string
+ *           format: date-time
+ *         expiresAt:
+ *           type: string
+ *           format: date-time
+ *         ipAddress:
+ *           type: string
+ *           nullable: true
+ *         userAgent:
+ *           type: string
+ *           nullable: true
+ *     AdminUser:
+ *       type: object
+ *       properties:
+ *         id:
+ *           type: string
+ *         email:
+ *           type: string
+ *         name:
+ *           type: string
+ *         apps:
+ *           type: array
+ *           items:
+ *             $ref: '#/components/schemas/AdminApp'
+ *         status:
+ *           type: string
+ *           enum: [aktiv, deaktiviert]
+ *           description: Derived - there is no status column.
+ *         createdAt:
+ *           type: string
+ *           format: date-time
+ *         lastSignInAt:
+ *           type: string
+ *           format: date-time
+ *           nullable: true
+ *           description: Newest session's creation time; null once every session has expired.
+ *     AdminUserDetail:
+ *       allOf:
+ *         - $ref: '#/components/schemas/AdminUser'
+ *         - type: object
+ *           properties:
+ *             sessions:
+ *               type: array
+ *               items:
+ *                 $ref: '#/components/schemas/AdminUserSession'
+ *             passkeyCount:
+ *               type: integer
+ *     AdminInvitation:
+ *       type: object
+ *       description: An open invitation. The token itself is never returned by any endpoint.
+ *       properties:
+ *         id:
+ *           type: integer
+ *         email:
+ *           type: string
+ *         name:
+ *           type: string
+ *         apps:
+ *           type: array
+ *           items:
+ *             $ref: '#/components/schemas/AdminApp'
+ *         invitedBy:
+ *           type: string
+ *           nullable: true
+ *           description: Null for the invitation created by the ADMIN_BOOTSTRAP_EMAIL bootstrap.
+ *         createdAt:
+ *           type: string
+ *           format: date-time
+ *         expiresAt:
+ *           type: string
+ *           format: date-time
+ */
+export {};

src/models/admin/admin.mail.ts

@@ -0,0 +1,124 @@
+import {MailService} from '../../common/common.mail.js';
+import {ADMIN_APP_URL} from './admin.config.js';
+
+/**
+ * The two transactional mails the admin module sends. Both go out through the
+ * shared MailService (Salesforce relay, see common.mail.ts), which never throws
+ * on a delivery failure - the invitation row and the reset token are already
+ * committed by the time we get here.
+ *
+ * HTML plus a plain-text body: the text part is not a fallback afterthought,
+ * it is what allowlist-based receivers and text-only clients actually show.
+ */
+
+const escapeHtml = (value: string): string => {
+	return value
+		.replace(/&/g, '&')
+		.replace(/</g, '&lt;')
+		.replace(/>/g, '&gt;')
+		.replace(/"/g, '&quot;');
+};
+
+// `heading` is escaped here; `paragraphs` are not, because callers pass markup
+// (a <strong> around the expiry date) and escape their own interpolations.
+const layout = (heading: string, paragraphs: string[], buttonLabel: string, buttonUrl: string): string => {
+	const body = paragraphs.map(p => `<p style="margin:0 0 16px;">${p}</p>`).join('');
+	return `<!doctype html>
+<html lang="de">
+<body style="margin:0;padding:24px;background:#f5f5f4;font-family:Helvetica,Arial,sans-serif;color:#1c1917;">
+<div style="max-width:520px;margin:0 auto;background:#ffffff;border-radius:8px;padding:32px;">
+<h1 style="margin:0 0 24px;font-size:20px;">${escapeHtml(heading)}</h1>
+${body}
+<p style="margin:24px 0;">
+<a href="${escapeHtml(buttonUrl)}" style="display:inline-block;background:#1c1917;color:#ffffff;text-decoration:none;padding:12px 20px;border-radius:6px;">${escapeHtml(buttonLabel)}</a>
+</p>
+<p style="margin:0;font-size:13px;color:#57534e;">Falls der Button nicht funktioniert, kopiere diesen Link in deinen Browser:<br>
+<span style="word-break:break-all;">${escapeHtml(buttonUrl)}</span></p>
+</div>
+</body>
+</html>`;
+};
+
+/**
+ * Invitation mail. The link carries the raw token in the query string; the
+ * admin app strips it from the URL as soon as it has read it (see the plan's
+ * §3b - the token must never reach an API access log or a Referer header).
+ */
+export const sendInvitationMail = async (
+	recipientAddress: string,
+	name: string,
+	token: string,
+	expiresAt: Date
+): Promise<boolean> => {
+	const url = `${ADMIN_APP_URL}/accept-invite?token=${encodeURIComponent(token)}`;
+	const expiry = expiresAt.toLocaleDateString('de-DE', {day: '2-digit', month: '2-digit', year: 'numeric'});
+	const subject = 'Dein Zugang zu Nachklang';
+
+	const text = [
+		`Hallo ${name},`,
+		'',
+		'du wurdest eingeladen, ein Nachklang-Konto anzulegen. Über diesen Link vergibst du dein Passwort:',
+		'',
+		url,
+		'',
+		`Der Link ist bis zum ${expiry} gültig.`,
+		'',
+		'Wenn du damit nichts anfangen kannst, ignoriere diese E-Mail einfach.',
+		'',
+		'Viele Grüße',
+		'Nachklang e.V.'
+	].join('\n');
+
+	const html = layout(
+		`Hallo ${name},`,
+		[
+			'du wurdest eingeladen, ein Nachklang-Konto anzulegen. Über den Button vergibst du dein Passwort.',
+			`Der Link ist bis zum <strong>${escapeHtml(expiry)}</strong> gültig.`,
+			'Wenn du damit nichts anfangen kannst, ignoriere diese E-Mail einfach.'
+		],
+		'Konto einrichten',
+		url
+	);
+
+	return MailService.sendMail(recipientAddress, subject, text, {html});
+};
+
+/**
+ * Password reset. better-auth builds the URL (it embeds its own token and the
+ * redirectTo the admin app passed), so this only wraps it in our templates.
+ */
+export const sendPasswordResetMail = async (
+	recipientAddress: string,
+	name: string,
+	url: string
+): Promise<boolean> => {
+	const subject = 'Passwort zurücksetzen';
+
+	const text = [
+		`Hallo ${name},`,
+		'',
+		'über diesen Link kannst du ein neues Passwort vergeben:',
+		'',
+		url,
+		'',
+		'Der Link ist eine Stunde gültig.',
+		'',
+		'Wenn du kein neues Passwort angefordert hast, ist nichts passiert - ignoriere diese E-Mail.',
+		'',
+		'Viele Grüße',
+		'Nachklang e.V.'
+	].join('\n');
+
+	const html = layout(
+		`Hallo ${name},`,
+		[
+			'über den Button kannst du ein neues Passwort vergeben.',
+			'Der Link ist eine Stunde gültig.',
+			'Wenn du kein neues Passwort angefordert hast, ist nichts passiert - ignoriere diese E-Mail.'
+		],
+		'Neues Passwort vergeben',
+		url
+	);
+
+	return MailService.sendMail(recipientAddress, subject, text, {html});
+};

src/models/admin/admin.middleware.ts

@@ -0,0 +1,140 @@
+import express from 'express';
+import {fromNodeHeaders} from 'better-auth/node';
+import {auth} from './admin.auth.js';
+import * as UsersService from './users/users.admin.service.js';
+import {AppName, AppPermission, AppRole} from './admin.schema.js';
+import {sendServerError} from './admin.errors.js';
+
+/**
+ * The one authenticator for every admin area in this API. It replaces
+ * feedback.auth.ts and tickets.auth.ts, which each re-implemented the same
+ * header-session check against the calendar users table.
+ *
+ * Two things are checked on every request, deliberately without any caching:
+ * that the session cookie is valid (better-auth), and that the user is still
+ * enabled and still holds the permission for this app (one database query).
+ * That is what makes "disable a user" and "revoke a session" take effect
+ * immediately rather than whenever a cached session happens to expire.
+ */
+
+// The shape the feedback and tickets services already expect - unchanged, so
+// nothing downstream of the authenticator needs to know this file replaced
+// their own.
+export interface AdminIdentity {
+	id: string;
+	email: string;
+	displayName: string;
+}
+
+export interface AdminAccess extends AdminIdentity {
+	disabled: boolean;
+	/** Every (app, role) grant. */
+	permissions: AppPermission[];
+	/** The distinct apps those grants cover. */
+	apps: AppName[];
+}
+
+const unauthorized = (res: express.Response): void => {
+	res.status(401).send({status: 'UNAUTHORIZED', message: 'Anmeldung erforderlich.'});
+};
+
+const forbidden = (res: express.Response, message: string): void => {
+	res.status(403).send({status: 'FORBIDDEN', message});
+};
+
+/**
+ * Resolves the session cookie to a user with their permissions, or null.
+ * One database query, no cache. Throws only on infrastructure errors.
+ */
+export const resolveAccess = async (req: express.Request): Promise<AdminAccess | null> => {
+	const session = await auth.api.getSession({headers: fromNodeHeaders(req.headers)});
+	if (!session?.user) {
+		return null;
+	}
+
+	const access = await UsersService.loadAccess(session.user.id);
+	if (!access) {
+		return null;
+	}
+
+	return {
+		id: access.id,
+		email: access.email,
+		displayName: access.displayName,
+		disabled: access.disabled,
+		permissions: access.permissions,
+		apps: access.apps
+	};
+};
+
+/**
+ * Any signed-in account, no permission required. Used by /admin/me and the
+ * account-management routes: a user with no app permissions at all still has
+ * to be able to see that, and to manage their own password and passkeys.
+ *
+ * The disabled check is not redundant with the session-create hook: that hook
+ * stops a disabled user from signing in, this stops one who was disabled while
+ * holding a live cookie. Disabling revokes sessions, so the window is small -
+ * but "small" is not "closed".
+ */
+export const requireSignedIn: express.RequestHandler = async (req, res, next) => {
+	try {
+		const access = await resolveAccess(req);
+		if (!access) {
+			unauthorized(res);
+			return;
+		}
+		if (access.disabled) {
+			forbidden(res, 'Dieses Konto ist deaktiviert.');
+			return;
+		}
+
+		res.locals.admin = access;
+		next();
+	} catch (e: any) {
+		sendServerError(res, e);
+	}
+};
+
+/**
+ * The gate every admin area sits behind. `requireAppAccess('feedback')` is
+ * what feedback.auth.ts's requireAdminAuth used to be, except that it now
+ * answers 403 for a signed-in user without that app's permission instead of
+ * letting any activated @nachklang.art account in.
+ *
+ * The optional second argument narrows it to one role within the app. Nothing
+ * passes it today - every app has exactly the `access` role - but it is the
+ * seam a finer permission arrives through.
+ */
+export const requireAppAccess = (app: AppName, role?: AppRole): express.RequestHandler => {
+	return async (req, res, next) => {
+		try {
+			const access = await resolveAccess(req);
+			if (!access) {
+				unauthorized(res);
+				return;
+			}
+			if (access.disabled) {
+				forbidden(res, 'Dieses Konto ist deaktiviert.');
+				return;
+			}
+
+			// Without a role this asks "may they open this app at all?", which is
+			// any grant on it. With one it asks for that specific grant - the hook
+			// a finer permission plugs into, without touching existing call sites.
+			const allowed = role === undefined
+				? access.apps.includes(app)
+				: access.permissions.some(permission => permission.app === app && permission.role === role);
+
+			if (!allowed) {
+				forbidden(res, 'Für diesen Bereich fehlt dir die Berechtigung.');
+				return;
+			}
+
+			res.locals.admin = access;
+			next();
+		} catch (e: any) {
+			sendServerError(res, e);
+		}
+	};
+};

src/models/admin/admin.schema.ts

@@ -0,0 +1,179 @@
+import {Generated} from 'kysely';
+
+/**
+ * Kysely table types for `nachklang_admin`. Only the columns this module
+ * actually reads or writes are declared - better-auth owns the full shape of
+ * its own tables and does not use this interface, it is here so the users and
+ * invitations services get compile-time checking instead of `any`.
+ *
+ * Column names follow better-auth's default "camel" casing for its tables
+ * (`emailVerified`, `userId`, `createdAt`); our own two tables use the
+ * snake_case convention of the rest of the repo's SQL.
+ */
+
+export type AppName = 'calendar' | 'feedback' | 'tickets' | 'admin';
+
+export const APP_NAMES: AppName[] = ['calendar', 'feedback', 'tickets', 'admin'];
+
+export const isAppName = (value: unknown): value is AppName => {
+	return typeof value === 'string' && (APP_NAMES as string[]).includes(value);
+};
+
+/**
+ * A permission is (app, role), not just an app. Today every app has exactly one
+ * role - `access`, "may use this app at all" - so the model looks like a plain
+ * list of apps and the UI renders one checkbox each. It is written this way
+ * anyway because the alternative gets expensive fast: `user_app_permissions`
+ * has primary key (user_id, app, role), so a user can hold several roles for
+ * the same app, and adding one later is a string in APP_ROLES plus rows - never
+ * a schema migration and never a change to the shape on the wire.
+ *
+ * Note the role is deliberately NOT called `admin`, which is what the column
+ * defaulted to before: on a `tickets` row that reads as "tickets administrator"
+ * when it only ever meant "has access", and once real roles exist there would
+ * be no way to tell the two apart.
+ */
+export const ACCESS_ROLE = 'access';
+
+export type AppRole = string;
+
+/** Every role that exists, per app, in display order. Extend to add one. */
+export const APP_ROLES: Record<AppName, readonly AppRole[]> = {
+	calendar: [ACCESS_ROLE],
+	feedback: [ACCESS_ROLE],
+	tickets: [ACCESS_ROLE],
+	admin: [ACCESS_ROLE]
+};
+
+export interface AppPermission {
+	app: AppName;
+	role: AppRole;
+}
+
+export const isAppRole = (app: AppName, role: unknown): role is AppRole => {
+	return typeof role === 'string' && APP_ROLES[app].includes(role);
+};
+
+export const isAppPermission = (value: unknown): value is AppPermission => {
+	if (typeof value !== 'object' || value === null) {
+		return false;
+	}
+	const candidate = value as {app?: unknown; role?: unknown};
+	return isAppName(candidate.app) && isAppRole(candidate.app, candidate.role);
+};
+
+/**
+ * Normalises whatever a caller sent into a valid, duplicate-free permission
+ * list. Accepts the richer `{app, role}` form and the plain `AppName` form,
+ * because `{apps: ['tickets']}` is still what the older callers send and it
+ * means exactly "tickets at the access role".
+ */
+export const toPermissions = (value: unknown): AppPermission[] | null => {
+	if (!Array.isArray(value)) {
+		return null;
+	}
+
+	const permissions: AppPermission[] = [];
+	for (const entry of value) {
+		if (isAppName(entry)) {
+			permissions.push({app: entry, role: ACCESS_ROLE});
+		} else if (isAppPermission(entry)) {
+			permissions.push({app: entry.app, role: entry.role});
+		} else {
+			return null;
+		}
+	}
+
+	const seen = new Set<string>();
+	return permissions.filter(permission => {
+		const key = `${permission.app}:${permission.role}`;
+		if (seen.has(key)) {
+			return false;
+		}
+		seen.add(key);
+		return true;
+	});
+};
+
+/** The distinct apps a permission list grants any access to. */
+export const appsOf = (permissions: AppPermission[]): AppName[] => {
+	return APP_NAMES.filter(app => permissions.some(permission => permission.app === app));
+};
+
+export interface UserTable {
+	id: string;
+	name: string;
+	email: string;
+	emailVerified: boolean;
+	image: string | null;
+	createdAt: Date;
+	updatedAt: Date;
+	// Added via better-auth `additionalFields` (see admin.auth.ts).
+	disabled: boolean;
+}
+
+export interface SessionTable {
+	id: string;
+	token: string;
+	userId: string;
+	expiresAt: Date;
+	createdAt: Date;
+	updatedAt: Date;
+	ipAddress: string | null;
+	userAgent: string | null;
+}
+
+export interface PasskeyTable {
+	id: string;
+	name: string | null;
+	userId: string;
+	createdAt: Date;
+}
+
+export interface UserAppPermissionTable {
+	user_id: string;
+	app: AppName;
+	role: AppRole;
+	granted_by: string | null;
+	granted_at: Generated<Date>;
+}
+
+export interface InvitationTable {
+	// AUTO_INCREMENT: present on select, never supplied on insert.
+	id: Generated<number>;
+	email: string;
+	name: string;
+	token_hash: string;
+	// JSON column holding an AppPermission[]. Older rows may hold a plain
+	// AppName[]; `parsePermissions` reads both.
+	permissions: string;
+	invited_by: string | null;
+	created_at: Generated<Date>;
+	expires_at: Date;
+	accepted_at: Date | null;
+	revoked_at: Date | null;
+}
+
+export interface VerificationTable {
+	id: string;
+	identifier: string;
+	value: string;
+	expiresAt: Date;
+}
+
+export interface RateLimitTable {
+	id: string;
+	key: string;
+	count: number;
+	lastRequest: number;
+}
+
+export interface AdminDatabase {
+	user: UserTable;
+	session: SessionTable;
+	passkey: PasskeyTable;
+	verification: VerificationTable;
+	rateLimit: RateLimitTable;
+	user_app_permissions: UserAppPermissionTable;
+	invitations: InvitationTable;
+}

src/models/admin/invitations/invitations.plugin.ts

@@ -0,0 +1,196 @@
+import * as z from 'zod';
+import {APIError, createAuthEndpoint} from 'better-auth/api';
+import {setSessionCookie} from 'better-auth/cookies';
+import {createLocalAccountIssuer} from 'better-auth/db';
+import {runWithTransaction} from '@better-auth/core/context';
+import type {BetterAuthPlugin} from 'better-auth';
+import * as InvitationsService from './invitations.service.js';
+import * as UsersService from '../users/users.admin.service.js';
+import logger from '../../../middleware/logger.js';
+
+/**
+ * The two public endpoints of the invitation flow, implemented as a better-auth
+ * plugin rather than as plain Express routes on the admin router.
+ *
+ * Why a plugin: `emailAndPassword.disableSignUp` is on, which makes
+ * `auth.api.signUpEmail` refuse - deliberately, there is no public sign-up.
+ * Accepting an invitation still has to create a user, hash a password, write a
+ * credential account and sign the person in. All four are better-auth
+ * internals reachable only from inside an endpoint's context, so this is where
+ * account creation lives. Nothing outside this file may create users.
+ *
+ * Because they are plugin endpoints they sit under better-auth's basePath:
+ *   POST /admin/auth/invitations/preview
+ *   POST /admin/auth/invitations/accept
+ *
+ * The token travels in the request *body*, never in the path or query, so it
+ * cannot end up in an access log or a Referer header.
+ */
+
+// Unknown, expired, revoked and already-accepted tokens must be
+// indistinguishable to the caller: one shared error, one shared message.
+const invalidToken = (): APIError => {
+	return new APIError('BAD_REQUEST', {
+		code: 'INVALID_INVITATION',
+		message: 'Diese Einladung ist nicht mehr gültig.'
+	});
+};
+
+export const invitationsPlugin = () => {
+	return {
+		id: 'nachklang-invitations',
+		endpoints: {
+			/**
+			 * Lets the accept-invite page show who the invitation is for before
+			 * asking for a password. Returns only name and email - never the
+			 * granted apps, which is information the invitee has no need for
+			 * and an attacker with a stolen link should not get either.
+			 */
+			previewInvitation: createAuthEndpoint(
+				'/invitations/preview',
+				{
+					method: 'POST',
+					body: z.object({
+						token: z.string().min(1)
+					})
+				},
+				async ctx => {
+					const invitation = await InvitationsService.findByToken(ctx.body.token);
+					if (!invitation) {
+						throw invalidToken();
+					}
+
+					return ctx.json({email: invitation.email, name: invitation.name});
+				}
+			),
+
+			/**
+			 * Redeems the invitation: creates the user, its credential account
+			 * and its permissions, then signs the person straight in so they
+			 * land in the app instead of on a login form.
+			 */
+			acceptInvitation: createAuthEndpoint(
+				'/invitations/accept',
+				{
+					method: 'POST',
+					body: z.object({
+						token: z.string().min(1),
+						password: z.string().min(8).max(128)
+					})
+				},
+				async ctx => {
+					const invitation = await InvitationsService.findByToken(ctx.body.token);
+					if (!invitation) {
+						throw invalidToken();
+					}
+
+					// An account for this address already exists: the right fix
+					// is for an admin to grant permissions on the existing user,
+					// not to create a second one. Reported distinctly because
+					// the person holds a valid token - this leaks nothing they
+					// do not already know about their own mailbox.
+					const existing = await UsersService.findUserByEmail(invitation.email);
+					if (existing) {
+						throw new APIError('CONFLICT', {
+							code: 'USER_ALREADY_EXISTS',
+							message: 'Für diese E-Mail-Adresse gibt es bereits ein Konto. Melde dich stattdessen an.'
+						});
+					}
+
+					// Claim the invitation before creating anything. The update
+					// is conditional on it still being open, so two concurrent
+					// submissions of the same link cannot both end up creating a
+					// user.
+					const claimed = await InvitationsService.markAccepted(invitation.id);
+					if (!claimed) {
+						throw invalidToken();
+					}
+
+					// The user and its credential account go in one better-auth
+					// transaction, the way better-auth's own sign-up route does
+					// it: a half-created account with no password is not
+					// recoverable through any route this API exposes.
+					//
+					// It cannot cover everything, though. `user_app_permissions`
+					// and `invitations` are written through this module's own
+					// Kysely pool, which is a different connection, so no single
+					// transaction spans both. What follows is therefore
+					// compensated by hand rather than rolled back.
+					let user: Awaited<ReturnType<typeof ctx.context.internalAdapter.createUser>> | null = null;
+					try {
+						user = await runWithTransaction(ctx.context.adapter, async () => {
+							const created = await ctx.context.internalAdapter.createUser(
+								{
+									email: invitation.email,
+									name: invitation.name,
+									// Accepting a link sent to that mailbox *is*
+									// the proof of address ownership, so there is
+									// no separate verification mail (plan
+									// decision 15).
+									emailVerified: true,
+									disabled: false
+								},
+								{method: 'email-password'}
+							);
+
+							// Same call better-auth's own sign-up route makes,
+							// down to the synthetic issuer - a credential account
+							// written any other way is not found on sign-in.
+							await ctx.context.internalAdapter.linkAccount({
+								userId: created.id,
+								providerId: 'credential',
+								issuer: createLocalAccountIssuer('credential'),
+								accountId: created.id,
+								password: await ctx.context.password.hash(ctx.body.password)
+							});
+
+							return created;
+						});
+
+						await UsersService.setPermissions(user.id, invitation.permissions, null);
+
+						const session = await ctx.context.internalAdapter.createSession(user.id);
+						await setSessionCookie(ctx, {session, user});
+
+						return ctx.json({
+							user: {id: user.id, email: user.email, name: user.name}
+						});
+					} catch (e: any) {
+						// Undo what committed, so the invitee can use their link
+						// again instead of being stranded with a burnt token, an
+						// account they cannot sign into, and an admin who cannot
+						// re-invite them (the create route 409s on an existing
+						// user, and there is no delete route by design).
+						//
+						// Deleting the user is safe here: it was created moments
+						// ago in this request, and acceptance already established
+						// that no account for this address existed before.
+						try {
+							if (user) {
+								await ctx.context.internalAdapter.deleteUser(user.id);
+							}
+							await InvitationsService.unmarkAccepted(invitation.id);
+						} catch (compensationError: any) {
+							// Now the state really is inconsistent, and only a
+							// human can sort it out. Say so loudly and precisely.
+							logger.error('Admin: invitation acceptance failed AND its rollback failed', {
+								invitationId: invitation.id,
+								email: invitation.email,
+								userId: user?.id,
+								detail: e?.message,
+								compensationDetail: compensationError?.message
+							});
+							throw e;
+						}
+
+						logger.error('Admin: invitation acceptance failed and was rolled back', {
+							invitationId: invitation.id,
+							detail: e?.message
+						});
+						throw e;
+					}
+				}
+			)
+		}
+	} satisfies BetterAuthPlugin;
+};

src/models/admin/invitations/invitations.router.ts

@@ -0,0 +1,208 @@
+import express, {Request, Response} from 'express';
+import * as InvitationsService from './invitations.service.js';
+import * as UsersService from '../users/users.admin.service.js';
+import {toPermissions} from '../admin.schema.js';
+import {sendInvitationMail} from '../admin.mail.js';
+import {ADMIN_APP_URL, LOG_INVITE_LINKS} from '../admin.config.js';
+import {sendServerError} from '../admin.errors.js';
+import logger from '../../../middleware/logger.js';
+
+export const invitationsRouter = express.Router();
+
+/**
+ * The admin-facing half of invitations (create, resend, revoke). The public
+ * half - preview and accept - lives in invitations.plugin.ts, because
+ * redeeming an invitation has to create a user through better-auth internals.
+ *
+ * Mounted behind requireAppAccess('admin').
+ */
+
+const EMAIL_PATTERN = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
+
+/**
+ * With the mail relay off (the normal local setup) the invitation mail never
+ * arrives, and only the token's hash is stored, so there would be no way to
+ * walk through the accept flow. Logging the link closes that.
+ *
+ * Gated on an explicit opt-in rather than on NODE_ENV: the link is a live
+ * account-creation credential, and "not production" is too weak a condition to
+ * hang that on. See LOG_INVITE_LINKS in admin.config.ts.
+ */
+const logInviteLinkInDev = (token: string): void => {
+	if (LOG_INVITE_LINKS) {
+		logger.info(`Admin: invitation link ${ADMIN_APP_URL}/accept-invite?token=${encodeURIComponent(token)}`);
+	}
+};
+
+/**
+ * @swagger
+ * /admin/invitations:
+ *      get:
+ *          summary: List open (unaccepted, unrevoked, unexpired) invitations
+ *          tags: [admin]
+ *          responses:
+ *              200:
+ *                  description: Success
+ */
+invitationsRouter.get('/', async (req: Request, res: Response) => {
+	try {
+		res.status(200).send(await InvitationsService.listOpenInvitations());
+	} catch (e: any) {
+		sendServerError(res, e);
+	}
+});
+
+/**
+ * @swagger
+ * /admin/invitations:
+ *      post:
+ *          summary: Invite someone and mail them an acceptance link
+ *          tags: [admin]
+ *          requestBody:
+ *              required: true
+ *              content:
+ *                  application/json:
+ *                      schema:
+ *                          type: object
+ *                          required: [email, name, permissions]
+ *                          properties:
+ *                              email:
+ *                                  type: string
+ *                              name:
+ *                                  type: string
+ *                              permissions:
+ *                                  type: array
+ *                                  description: >
+ *                                      One entry per (app, role). A plain array of app names is
+ *                                      accepted too and means the same at the `access` role.
+ *                                  items:
+ *                                      type: object
+ *                                      properties:
+ *                                          app:
+ *                                              type: string
+ *                                          role:
+ *                                              type: string
+ *          responses:
+ *              201:
+ *                  description: Invitation created and mailed
+ *              400:
+ *                  description: Invalid input
+ *              409:
+ *                  description: A user with this address already exists
+ */
+invitationsRouter.post('/', async (req: Request, res: Response) => {
+	try {
+		const email = String(req.body?.email || '').trim().toLowerCase();
+		const name = String(req.body?.name || '').trim();
+
+		// Same two accepted shapes as PUT /admin/users/:id/permissions.
+		const permissions = toPermissions(req.body?.permissions ?? req.body?.apps);
+
+		if (!EMAIL_PATTERN.test(email) || name.length === 0 || !permissions) {
+			res.status(400).send({
+				status: 'BAD_REQUEST',
+				message: 'E-Mail, Name und Berechtigungen sind erforderlich.'
+			});
+			return;
+		}
+
+		// Inviting someone who already has an account would strand them on an
+		// accept page that can only fail. Granting permissions on the existing
+		// user is the operation they actually want.
+		if (await UsersService.findUserByEmail(email)) {
+			res.status(409).send({
+				status: 'CONFLICT',
+				message: 'Für diese E-Mail-Adresse gibt es bereits ein Konto. Vergib dort die Berechtigungen.'
+			});
+			return;
+		}
+
+		const invitation = await InvitationsService.createInvitation(
+			email,
+			name,
+			permissions,
+			res.locals.admin.id
+		);
+
+		const mailed = await sendInvitationMail(email, name, invitation.token, invitation.expiresAt);
+		if (!mailed) {
+			logger.warn('Admin: invitation created but the mail was not accepted', {email});
+		}
+		logInviteLinkInDev(invitation.token);
+
+		res.status(201).send({id: invitation.id, email, name, expiresAt: invitation.expiresAt, mailed});
+	} catch (e: any) {
+		sendServerError(res, e);
+	}
+});
+
+/**
+ * @swagger
+ * /admin/invitations/{invitationId}/resend:
+ *      post:
+ *          summary: Issue a new token for an open invitation and mail it again
+ *          description: The previous link stops working.
+ *          tags: [admin]
+ *          responses:
+ *              200:
+ *                  description: Resent
+ *              404:
+ *                  description: No open invitation with this id
+ */
+invitationsRouter.post('/:invitationId/resend', async (req: Request, res: Response) => {
+	try {
+		const invitationId = parseInt(req.params.invitationId, 10);
+		if (Number.isNaN(invitationId)) {
+			res.status(400).send({status: 'BAD_REQUEST', message: 'Ungültige Einladungs-ID.'});
+			return;
+		}
+
+		const resent = await InvitationsService.resendInvitation(invitationId);
+		if (!resent) {
+			res.status(404).send({status: 'NOT_FOUND', message: 'Einladung nicht gefunden.'});
+			return;
+		}
+
+		const mailed = await sendInvitationMail(resent.email, resent.name, resent.token, resent.expiresAt);
+		if (!mailed) {
+			logger.warn('Admin: invitation resent but the mail was not accepted', {email: resent.email});
+		}
+		logInviteLinkInDev(resent.token);
+
+		res.status(200).send({id: invitationId, expiresAt: resent.expiresAt, mailed});
+	} catch (e: any) {
+		sendServerError(res, e);
+	}
+});
+
+/**
+ * @swagger
+ * /admin/invitations/{invitationId}:
+ *      delete:
+ *          summary: Revoke an open invitation
+ *          tags: [admin]
+ *          responses:
+ *              204:
+ *                  description: Revoked
+ *              404:
+ *                  description: No open invitation with this id
+ */
+invitationsRouter.delete('/:invitationId', async (req: Request, res: Response) => {
+	try {
+		const invitationId = parseInt(req.params.invitationId, 10);
+		if (Number.isNaN(invitationId)) {
+			res.status(400).send({status: 'BAD_REQUEST', message: 'Ungültige Einladungs-ID.'});
+			return;
+		}
+
+		const revoked = await InvitationsService.revokeInvitation(invitationId);
+		if (!revoked) {
+			res.status(404).send({status: 'NOT_FOUND', message: 'Einladung nicht gefunden.'});
+			return;
+		}
+
+		res.status(204).send();
+	} catch (e: any) {
+		sendServerError(res, e);
+	}
+});

src/models/admin/invitations/invitations.service.ts

@@ -0,0 +1,239 @@
+import * as crypto from 'crypto';
+import {NachklangAdminDB} from '../Admin.db.js';
+import {AppPermission, isAppName, isAppPermission, ACCESS_ROLE} from '../admin.schema.js';
+
+const db = NachklangAdminDB.db;
+
+/**
+ * Invitations are this API's only path to a new account (there is no public
+ * sign-up). The raw token exists exactly twice: in the mail we send and in the
+ * request body when it comes back. What we store is its SHA-256 hash, so a
+ * database dump does not hand out account access - the same reasoning as the
+ * calendar module's session key hashing, and the reason lookups go through
+ * `findByToken` rather than any query on a plaintext column.
+ */
+
+export const INVITATION_TTL_DAYS = 7;
+
+export interface OpenInvitation {
+	id: number;
+	email: string;
+	name: string;
+	permissions: AppPermission[];
+	invitedBy: string | null;
+	createdAt: Date;
+	expiresAt: Date;
+}
+
+export interface AcceptableInvitation {
+	id: number;
+	email: string;
+	name: string;
+	permissions: AppPermission[];
+}
+
+const hashToken = (token: string): string => {
+	return crypto.createHash('sha256').update(token).digest('hex');
+};
+
+const generateToken = (): string => {
+	// 32 bytes, url-safe: it travels in a mail link's query string.
+	return crypto.randomBytes(32).toString('base64url');
+};
+
+/**
+ * Reads the stored permission list. Two shapes are accepted: the current
+ * `[{app, role}]`, and a bare `['tickets', ...]` from before roles existed,
+ * which means the same thing at the `access` role. Invitations live for seven
+ * days, so a deploy that changes the shape has in-flight rows in the old one -
+ * tolerating both is what stops those invitees from being stranded.
+ *
+ * mysql2 hands back a JSON column already parsed; a driver or column-type
+ * change that turns it into a string must not break the read path either.
+ */
+const parsePermissions = (value: unknown): AppPermission[] => {
+	const raw = typeof value === 'string' ? JSON.parse(value) : value;
+	if (!Array.isArray(raw)) {
+		return [];
+	}
+
+	return raw.flatMap((entry): AppPermission[] => {
+		if (isAppName(entry)) {
+			return [{app: entry, role: ACCESS_ROLE}];
+		}
+		return isAppPermission(entry) ? [{app: entry.app, role: entry.role}] : [];
+	});
+};
+
+const expiryFromNow = (): Date => {
+	return new Date(Date.now() + INVITATION_TTL_DAYS * 24 * 60 * 60 * 1000);
+};
+
+/**
+ * Creates an invitation and returns the raw token for the mail. Any earlier
+ * open invitation for the same address is revoked first: two valid links for
+ * one mailbox is a needless second live credential, and "resend" would
+ * otherwise quietly accumulate them.
+ */
+export const createInvitation = async (
+	email: string,
+	name: string,
+	permissions: AppPermission[],
+	invitedBy: string | null
+): Promise<{id: number; token: string; expiresAt: Date}> => {
+	const token = generateToken();
+	const expiresAt = expiryFromNow();
+	const valid = permissions.filter(isAppPermission);
+
+	const id = await db.transaction().execute(async trx => {
+		await trx
+			.updateTable('invitations')
+			.set({revoked_at: new Date()})
+			.where('email', '=', email)
+			.where('accepted_at', 'is', null)
+			.where('revoked_at', 'is', null)
+			.execute();
+
+		const result = await trx
+			.insertInto('invitations')
+			.values({
+				email,
+				name,
+				token_hash: hashToken(token),
+				permissions: JSON.stringify(valid),
+				invited_by: invitedBy,
+				created_at: new Date(),
+				expires_at: expiresAt
+			})
+			.executeTakeFirst();
+
+		return Number(result.insertId);
+	});
+
+	return {id, token, expiresAt};
+};
+
+/**
+ * Looks up a still-usable invitation by raw token. Callers must not
+ * distinguish "unknown", "expired", "revoked" and "already accepted" to the
+ * client: all four answer with the same shape, so a stranger cannot probe which
+ * tokens ever existed.
+ */
+export const findByToken = async (token: string): Promise<AcceptableInvitation | null> => {
+	const row = await db
+		.selectFrom('invitations')
+		.select(['id', 'email', 'name', 'permissions'])
+		.where('token_hash', '=', hashToken(token))
+		.where('accepted_at', 'is', null)
+		.where('revoked_at', 'is', null)
+		.where('expires_at', '>', new Date())
+		.executeTakeFirst();
+
+	if (!row) {
+		return null;
+	}
+
+	return {id: row.id, email: row.email, name: row.name, permissions: parsePermissions(row.permissions)};
+};
+
+/** Marks the invitation accepted. Conditional on it still being open so two
+ *  concurrent accepts of the same link cannot both create an account. */
+export const markAccepted = async (invitationId: number): Promise<boolean> => {
+	const result = await db
+		.updateTable('invitations')
+		.set({accepted_at: new Date()})
+		.where('id', '=', invitationId)
+		.where('accepted_at', 'is', null)
+		.where('revoked_at', 'is', null)
+		.executeTakeFirst();
+
+	return Number(result.numUpdatedRows) > 0;
+};
+
+/**
+ * Reverses markAccepted. Used only to compensate a failed acceptance: the user
+ * could not be created, so the link must become usable again rather than
+ * stranding the invitee with a burnt token and no account.
+ */
+export const unmarkAccepted = async (invitationId: number): Promise<void> => {
+	await db
+		.updateTable('invitations')
+		.set({accepted_at: null})
+		.where('id', '=', invitationId)
+		.execute();
+};
+
+export const listOpenInvitations = async (): Promise<OpenInvitation[]> => {
+	const rows = await db
+		.selectFrom('invitations')
+		.select(['id', 'email', 'name', 'permissions', 'invited_by', 'created_at', 'expires_at'])
+		.where('accepted_at', 'is', null)
+		.where('revoked_at', 'is', null)
+		.where('expires_at', '>', new Date())
+		.orderBy('created_at', 'desc')
+		.execute();
+
+	return rows.map(row => ({
+		id: row.id,
+		email: row.email,
+		name: row.name,
+		permissions: parsePermissions(row.permissions),
+		invitedBy: row.invited_by,
+		createdAt: row.created_at,
+		expiresAt: row.expires_at
+	}));
+};
+
+export const getOpenInvitation = async (invitationId: number): Promise<OpenInvitation | null> => {
+	const all = await listOpenInvitations();
+	return all.find(invitation => invitation.id === invitationId) ?? null;
+};
+
+/** Resend issues a *new* token and expiry and invalidates the old one, rather
+ *  than re-mailing the existing link: if the first mail leaked, resending it
+ *  would extend the leak's lifetime. */
+export const resendInvitation = async (
+	invitationId: number
+): Promise<{token: string; email: string; name: string; expiresAt: Date} | null> => {
+	const invitation = await getOpenInvitation(invitationId);
+	if (!invitation) {
+		return null;
+	}
+
+	const token = generateToken();
+	const expiresAt = expiryFromNow();
+
+	await db
+		.updateTable('invitations')
+		.set({token_hash: hashToken(token), expires_at: expiresAt, created_at: new Date()})
+		.where('id', '=', invitationId)
+		.execute();
+
+	return {token, email: invitation.email, name: invitation.name, expiresAt};
+};
+
+export const revokeInvitation = async (invitationId: number): Promise<boolean> => {
+	const result = await db
+		.updateTable('invitations')
+		.set({revoked_at: new Date()})
+		.where('id', '=', invitationId)
+		.where('accepted_at', 'is', null)
+		.where('revoked_at', 'is', null)
+		.executeTakeFirst();
+
+	return Number(result.numUpdatedRows) > 0;
+};
+
+/** Used by the bootstrap to stay idempotent across restarts. */
+export const hasOpenInvitationFor = async (email: string): Promise<boolean> => {
+	const row = await db
+		.selectFrom('invitations')
+		.select('id')
+		.where('email', '=', email)
+		.where('accepted_at', 'is', null)
+		.where('revoked_at', 'is', null)
+		.where('expires_at', '>', new Date())
+		.executeTakeFirst();
+
+	return Boolean(row);
+};

src/models/admin/users/users.admin.router.ts

@@ -0,0 +1,247 @@
+import express, {Request, Response} from 'express';
+import * as UsersService from './users.admin.service.js';
+import {toPermissions} from '../admin.schema.js';
+import {sendServerError} from '../admin.errors.js';
+
+export const usersAdminRouter = express.Router();
+
+/**
+ * User administration. Mounted behind requireAppAccess('admin'), so every
+ * handler here can assume res.locals.admin is an admin.
+ *
+ * The guards below exist because this API can lock its own operators out: the
+ * only way to grant a permission is through these routes, so an admin who
+ * removes the last `admin` permission leaves nobody who can put it back short
+ * of a manual SQL statement in production.
+ */
+
+const conflict = (res: Response, message: string): void => {
+	res.status(409).send({status: 'CONFLICT', message});
+};
+
+const notFound = (res: Response): void => {
+	res.status(404).send({status: 'NOT_FOUND', message: 'Benutzer nicht gefunden.'});
+};
+
+/**
+ * @swagger
+ * /admin/users:
+ *      get:
+ *          summary: List all users with their app permissions and status
+ *          tags: [admin]
+ *          responses:
+ *              200:
+ *                  description: Success
+ *              401:
+ *                  description: Not signed in
+ *              403:
+ *                  description: Missing the admin permission
+ */
+usersAdminRouter.get('/', async (req: Request, res: Response) => {
+	try {
+		res.status(200).send(await UsersService.listUsers());
+	} catch (e: any) {
+		sendServerError(res, e);
+	}
+});
+
+/**
+ * @swagger
+ * /admin/users/{userId}:
+ *      get:
+ *          summary: One user with their active sessions and passkey count
+ *          tags: [admin]
+ *          parameters:
+ *              - in: path
+ *                name: userId
+ *                required: true
+ *                schema:
+ *                    type: string
+ *          responses:
+ *              200:
+ *                  description: Success
+ *              404:
+ *                  description: Unknown user
+ */
+usersAdminRouter.get('/:userId', async (req: Request, res: Response) => {
+	try {
+		const detail = await UsersService.getUserDetail(req.params.userId);
+		if (!detail) {
+			notFound(res);
+			return;
+		}
+		res.status(200).send(detail);
+	} catch (e: any) {
+		sendServerError(res, e);
+	}
+});
+
+/**
+ * @swagger
+ * /admin/users/{userId}/permissions:
+ *      put:
+ *          summary: Replace a user's app permissions
+ *          description: Refuses to remove the caller's own admin permission or the last remaining active admin.
+ *          tags: [admin]
+ *          requestBody:
+ *              required: true
+ *              content:
+ *                  application/json:
+ *                      schema:
+ *                          type: object
+ *                          properties:
+ *                              permissions:
+ *                                  type: array
+ *                                  description: >
+ *                                      One entry per (app, role). `access` is the only role today.
+ *                                      A plain array of app names is also accepted and means the
+ *                                      same at the `access` role.
+ *                                  items:
+ *                                      type: object
+ *                                      properties:
+ *                                          app:
+ *                                              type: string
+ *                                              enum: [calendar, feedback, tickets, admin]
+ *                                          role:
+ *                                              type: string
+ *                                              enum: [access]
+ *          responses:
+ *              200:
+ *                  description: Success
+ *              400:
+ *                  description: Invalid app or role
+ *              409:
+ *                  description: Would lock the last admin out
+ */
+usersAdminRouter.put('/:userId/permissions', async (req: Request, res: Response) => {
+	try {
+		const userId = req.params.userId;
+
+		// `permissions: [{app, role}]` is the real shape; `apps: ['tickets']` is
+		// accepted as shorthand for the same thing at the `access` role, so a
+		// caller that predates roles keeps working.
+		const permissions = toPermissions(req.body?.permissions ?? req.body?.apps);
+
+		if (!permissions) {
+			res.status(400).send({status: 'BAD_REQUEST', message: 'Ungültige Berechtigungsliste.'});
+			return;
+		}
+
+		if (!(await UsersService.userExists(userId))) {
+			notFound(res);
+			return;
+		}
+
+		const target = await UsersService.loadAccess(userId);
+		const keepsAdmin = permissions.some(permission => permission.app === 'admin');
+		const losesAdmin = Boolean(target?.apps.includes('admin')) && !keepsAdmin;
+
+		// Self-lockout is checked here because it needs the caller's identity,
+		// which the service has no business knowing. The last-admin check is
+		// NOT done here: it has to be inside the write transaction to survive
+		// two admins acting at the same time (see setPermissionsGuarded).
+		if (losesAdmin && userId === res.locals.admin.id) {
+			conflict(res, 'Du kannst dir die Admin-Berechtigung nicht selbst entziehen.');
+			return;
+		}
+
+		const result = await UsersService.setPermissionsGuarded(userId, permissions, res.locals.admin.id);
+		if (result === 'last-admin') {
+			conflict(res, 'Die letzte Admin-Berechtigung kann nicht entzogen werden.');
+			return;
+		}
+
+		res.status(200).send(await UsersService.getUserDetail(userId));
+	} catch (e: any) {
+		sendServerError(res, e);
+	}
+});
+
+/**
+ * @swagger
+ * /admin/users/{userId}/disable:
+ *      post:
+ *          summary: Disable a user and revoke all of their sessions
+ *          tags: [admin]
+ *          responses:
+ *              200:
+ *                  description: Success
+ *              409:
+ *                  description: Would disable the caller or the last admin
+ */
+usersAdminRouter.post('/:userId/disable', async (req: Request, res: Response) => {
+	try {
+		const userId = req.params.userId;
+
+		if (userId === res.locals.admin.id) {
+			conflict(res, 'Du kannst dich nicht selbst deaktivieren.');
+			return;
+		}
+
+		const target = await UsersService.loadAccess(userId);
+		if (!target) {
+			notFound(res);
+			return;
+		}
+
+		const result = await UsersService.disableUserGuarded(userId);
+		if (result === 'last-admin') {
+			conflict(res, 'Der letzte aktive Admin kann nicht deaktiviert werden.');
+			return;
+		}
+
+		res.status(200).send(await UsersService.getUserDetail(userId));
+	} catch (e: any) {
+		sendServerError(res, e);
+	}
+});
+
+/**
+ * @swagger
+ * /admin/users/{userId}/enable:
+ *      post:
+ *          summary: Re-enable a disabled user
+ *          description: Does not restore sessions - the user signs in again.
+ *          tags: [admin]
+ *          responses:
+ *              200:
+ *                  description: Success
+ */
+usersAdminRouter.post('/:userId/enable', async (req: Request, res: Response) => {
+	try {
+		if (!(await UsersService.userExists(req.params.userId))) {
+			notFound(res);
+			return;
+		}
+
+		await UsersService.enableUser(req.params.userId);
+		res.status(200).send(await UsersService.getUserDetail(req.params.userId));
+	} catch (e: any) {
+		sendServerError(res, e);
+	}
+});
+
+/**
+ * @swagger
+ * /admin/users/{userId}/sessions/{sessionId}:
+ *      delete:
+ *          summary: Revoke one session of a user
+ *          tags: [admin]
+ *          responses:
+ *              204:
+ *                  description: Revoked
+ *              404:
+ *                  description: Unknown session for this user
+ */
+usersAdminRouter.delete('/:userId/sessions/:sessionId', async (req: Request, res: Response) => {
+	try {
+		const revoked = await UsersService.revokeSession(req.params.userId, req.params.sessionId);
+		if (!revoked) {
+			res.status(404).send({status: 'NOT_FOUND', message: 'Sitzung nicht gefunden.'});
+			return;
+		}
+		res.status(204).send();
+	} catch (e: any) {
+		sendServerError(res, e);
+	}
+});

src/models/admin/users/users.admin.service.ts

@@ -0,0 +1,439 @@
+import {Transaction} from 'kysely';
+import {NachklangAdminDB} from '../Admin.db.js';
+import {
+	AdminDatabase,
+	AppName,
+	AppPermission,
+	AppRole,
+	ACCESS_ROLE,
+	appsOf,
+	isAppName,
+	isAppRole
+} from '../admin.schema.js';
+
+const db = NachklangAdminDB.db;
+
+/**
+ * Everything that reads or writes permissions. Two callers with very different
+ * hot-path requirements share this file: admin.middleware.ts runs
+ * `loadAccess` on *every* admin-authenticated request (which is why it is one
+ * query joining `user.disabled` and the permission rows - see the plan's
+ * decision to run without better-auth's cookieCache), and the /admin/users
+ * routes run the rest.
+ */
+
+export interface UserAccess {
+	id: string;
+	email: string;
+	displayName: string;
+	disabled: boolean;
+	/** Every (app, role) grant this user holds. */
+	permissions: AppPermission[];
+	/** The distinct apps the above grants any access to. Derived, kept because
+	 *  most callers only ever ask "may they open this app at all?". */
+	apps: AppName[];
+}
+
+export type UserStatus = 'aktiv' | 'deaktiviert';
+
+export interface UserListEntry {
+	id: string;
+	email: string;
+	name: string;
+	permissions: AppPermission[];
+	apps: AppName[];
+	status: UserStatus;
+	createdAt: Date;
+	lastSignInAt: Date | null;
+}
+
+export interface UserSessionEntry {
+	id: string;
+	createdAt: Date;
+	expiresAt: Date;
+	ipAddress: string | null;
+	userAgent: string | null;
+}
+
+export interface UserDetail extends UserListEntry {
+	sessions: UserSessionEntry[];
+	passkeyCount: number;
+}
+
+/**
+ * The single per-request lookup behind requireAppAccess. Returns null when the
+ * user row is gone; `disabled` is returned rather than filtered so the
+ * middleware can answer 403 (account deactivated) instead of a misleading 401.
+ */
+export const loadAccess = async (userId: string): Promise<UserAccess | null> => {
+	const rows = await db
+		.selectFrom('user')
+		.leftJoin('user_app_permissions', 'user_app_permissions.user_id', 'user.id')
+		.where('user.id', '=', userId)
+		.select([
+			'user.id as id',
+			'user.email as email',
+			'user.name as name',
+			'user.disabled as disabled',
+			'user_app_permissions.app as app',
+			'user_app_permissions.role as role'
+		])
+		.execute();
+
+	if (rows.length === 0) {
+		return null;
+	}
+
+	const permissions = toPermissionRows(rows);
+
+	return {
+		id: rows[0].id,
+		email: rows[0].email,
+		displayName: rows[0].name,
+		// MySQL TINYINT(1) comes back as 0/1 through mysql2.
+		disabled: Boolean(rows[0].disabled),
+		permissions,
+		apps: appsOf(permissions)
+	};
+};
+
+/**
+ * Turns joined permission rows into AppPermission[]. The left join produces one
+ * row with a null app for a user who holds nothing, and a role written directly
+ * into the database that no longer appears in APP_ROLES is dropped rather than
+ * trusted - the table is the store, APP_ROLES is the contract.
+ */
+const toPermissionRows = (rows: {app: AppName | null; role: string | null}[]): AppPermission[] => {
+	return rows
+		.filter((row): row is {app: AppName; role: string} =>
+			isAppName(row.app) && isAppRole(row.app, row.role))
+		.map(row => ({app: row.app, role: row.role}));
+};
+
+export const listUsers = async (): Promise<UserListEntry[]> => {
+	const users = await db
+		.selectFrom('user')
+		.select(['id', 'email', 'name', 'disabled', 'createdAt'])
+		.orderBy('name', 'asc')
+		.execute();
+
+	const permissions = await db
+		.selectFrom('user_app_permissions')
+		.select(['user_id', 'app', 'role'])
+		.execute();
+
+	// Last sign-in is derived from the newest session rather than stored: a
+	// session row is created on every sign-in and we never update its
+	// createdAt, so max(createdAt) is exactly that, with no extra column to
+	// keep in sync.
+	//
+	// The expiry filter must match getUserDetail's. better-auth only deletes an
+	// expired session when someone actually presents it, so expired rows linger
+	// - without this, the list would report a last sign-in for someone the
+	// detail view shows as never having signed in.
+	const lastSessions = await db
+		.selectFrom('session')
+		.where('expiresAt', '>', new Date())
+		.select(({fn}) => ['userId', fn.max('createdAt').as('lastSignInAt')])
+		.groupBy('userId')
+		.execute();
+
+	const permissionsByUser = new Map<string, AppPermission[]>();
+	for (const row of permissions) {
+		if (!isAppRole(row.app, row.role)) {
+			continue;
+		}
+		const held = permissionsByUser.get(row.user_id) || [];
+		held.push({app: row.app, role: row.role});
+		permissionsByUser.set(row.user_id, held);
+	}
+
+	const lastSignInByUser = new Map<string, Date | null>(
+		lastSessions.map(row => [row.userId, row.lastSignInAt as Date | null])
+	);
+
+	return users.map(user => {
+		const held = permissionsByUser.get(user.id) || [];
+		return {
+			id: user.id,
+			email: user.email,
+			name: user.name,
+			permissions: held,
+			apps: appsOf(held),
+			status: user.disabled ? ('deaktiviert' as const) : ('aktiv' as const),
+			createdAt: user.createdAt,
+			lastSignInAt: lastSignInByUser.get(user.id) ?? null
+		};
+	});
+};
+
+export const getUserDetail = async (userId: string): Promise<UserDetail | null> => {
+	const user = await db
+		.selectFrom('user')
+		.select(['id', 'email', 'name', 'disabled', 'createdAt'])
+		.where('id', '=', userId)
+		.executeTakeFirst();
+
+	if (!user) {
+		return null;
+	}
+
+	const [permissions, sessions, passkeys] = await Promise.all([
+		db
+			.selectFrom('user_app_permissions')
+			.select(['app', 'role'])
+			.where('user_id', '=', userId)
+			.execute(),
+		db
+			.selectFrom('session')
+			.select(['id', 'createdAt', 'expiresAt', 'ipAddress', 'userAgent'])
+			.where('userId', '=', userId)
+			.where('expiresAt', '>', new Date())
+			.orderBy('createdAt', 'desc')
+			.execute(),
+		db
+			.selectFrom('passkey')
+			.select(({fn}) => fn.countAll<number>().as('count'))
+			.where('userId', '=', userId)
+			.executeTakeFirst()
+	]);
+
+	const held = toPermissionRows(permissions);
+
+	return {
+		id: user.id,
+		email: user.email,
+		name: user.name,
+		permissions: held,
+		apps: appsOf(held),
+		status: user.disabled ? 'deaktiviert' : 'aktiv',
+		createdAt: user.createdAt,
+		lastSignInAt: sessions.length > 0 ? sessions[0].createdAt : null,
+		sessions,
+		passkeyCount: Number(passkeys?.count ?? 0)
+	};
+};
+
+/**
+ * Replaces a user's permission set. Written as delete-then-insert inside one
+ * transaction rather than a diff: the set is at most four rows, and a diff
+ * would only add branches for no measurable gain.
+ */
+
+/** The rows a permission list becomes. One row per (app, role). */
+const permissionRows = (
+	userId: string,
+	permissions: AppPermission[],
+	grantedBy: string | null
+) => {
+	return permissions.map(permission => ({
+		user_id: userId,
+		app: permission.app,
+		role: permission.role,
+		granted_by: grantedBy,
+		granted_at: new Date()
+	}));
+};
+
+/** Drops anything not in APP_ROLES and de-duplicates on (app, role). */
+const validPermissions = (permissions: AppPermission[]): AppPermission[] => {
+	const seen = new Set<string>();
+	return permissions.filter(permission => {
+		if (!isAppName(permission.app) || !isAppRole(permission.app, permission.role)) {
+			return false;
+		}
+		const key = `${permission.app}:${permission.role}`;
+		if (seen.has(key)) {
+			return false;
+		}
+		seen.add(key);
+		return true;
+	});
+};
+
+export const setPermissions = async (
+	userId: string,
+	permissions: AppPermission[],
+	grantedBy: string | null
+): Promise<void> => {
+	const valid = validPermissions(permissions);
+
+	await db.transaction().execute(async trx => {
+		await trx.deleteFrom('user_app_permissions').where('user_id', '=', userId).execute();
+		if (valid.length > 0) {
+			await trx
+				.insertInto('user_app_permissions')
+				.values(permissionRows(userId, valid, grantedBy))
+				.execute();
+		}
+	});
+};
+
+/**
+ * Why the guards live down here rather than in the router: they are
+ * check-then-act, and the check has to happen inside the same transaction as
+ * the write, over locked rows. Two admins each removing the other's `admin`
+ * permission at the same moment would otherwise both read a count of 2, both
+ * pass, and both commit - leaving nobody who can administer anything, with
+ * ADMIN_BOOTSTRAP_EMAIL at the next restart as the only way back in.
+ *
+ * `SELECT ... FOR UPDATE` makes the second transaction wait and re-read the
+ * count the first one just changed.
+ */
+export type LastAdminGuardResult = 'ok' | 'last-admin';
+
+const countActiveAdminsForUpdate = async (trx: Transaction<AdminDatabase>): Promise<number> => {
+	const row = await trx
+		.selectFrom('user_app_permissions')
+		.innerJoin('user', 'user.id', 'user_app_permissions.user_id')
+		.where('user_app_permissions.app', '=', 'admin')
+		.where('user.disabled', '=', false)
+		// countDistinct, not countAll: with (user_id, app, role) as the key one
+		// user can hold several roles on `admin`, and counting rows would make a
+		// single admin with two roles look like two admins - defeating the guard
+		// at exactly the moment it matters.
+		.select(({fn}) => fn.count<number>('user_app_permissions.user_id').distinct().as('count'))
+		.forUpdate()
+		.executeTakeFirst();
+
+	return Number(row?.count ?? 0);
+};
+
+/**
+ * Replaces a user's permissions, refusing to remove the last active admin.
+ * Returns 'last-admin' instead of throwing so the router can answer 409.
+ */
+export const setPermissionsGuarded = async (
+	userId: string,
+	permissions: AppPermission[],
+	grantedBy: string | null
+): Promise<LastAdminGuardResult> => {
+	const valid = validPermissions(permissions);
+	const keepsAdmin = valid.some(permission => permission.app === 'admin');
+
+	return db.transaction().execute(async trx => {
+		const target = await trx
+			.selectFrom('user_app_permissions')
+			.innerJoin('user', 'user.id', 'user_app_permissions.user_id')
+			.where('user_app_permissions.user_id', '=', userId)
+			.where('user_app_permissions.app', '=', 'admin')
+			.select(['user.disabled as disabled'])
+			.limit(1)
+			.forUpdate()
+			.executeTakeFirst();
+
+		const losesAdmin = Boolean(target) && !keepsAdmin;
+		if (losesAdmin && !target?.disabled && (await countActiveAdminsForUpdate(trx)) <= 1) {
+			return 'last-admin';
+		}
+
+		await trx.deleteFrom('user_app_permissions').where('user_id', '=', userId).execute();
+		if (valid.length > 0) {
+			await trx
+				.insertInto('user_app_permissions')
+				.values(permissionRows(userId, valid, grantedBy))
+				.execute();
+		}
+
+		return 'ok';
+	});
+};
+
+/**
+ * Disables a user and revokes every session, refusing to disable the last
+ * active admin. Same locking rationale as setPermissionsGuarded.
+ */
+export const disableUserGuarded = async (userId: string): Promise<LastAdminGuardResult> => {
+	return db.transaction().execute(async trx => {
+		const isAdmin = await trx
+			.selectFrom('user_app_permissions')
+			.innerJoin('user', 'user.id', 'user_app_permissions.user_id')
+			.where('user_app_permissions.user_id', '=', userId)
+			.where('user_app_permissions.app', '=', 'admin')
+			.where('user.disabled', '=', false)
+			.select('user_app_permissions.user_id')
+			.limit(1)
+			.forUpdate()
+			.executeTakeFirst();
+
+		if (isAdmin && (await countActiveAdminsForUpdate(trx)) <= 1) {
+			return 'last-admin';
+		}
+
+		await trx.updateTable('user').set({disabled: true}).where('id', '=', userId).execute();
+		await trx.deleteFrom('session').where('userId', '=', userId).execute();
+
+		return 'ok';
+	});
+};
+
+export const grantPermission = async (
+	userId: string,
+	app: AppName,
+	grantedBy: string | null,
+	role: AppRole = ACCESS_ROLE
+): Promise<void> => {
+	await db
+		.insertInto('user_app_permissions')
+		.values({user_id: userId, app, role, granted_by: grantedBy, granted_at: new Date()})
+		// The row already existing is the success case - this is "make sure they
+		// hold it", not "re-grant it" - so nothing is overwritten and granted_by
+		// keeps naming whoever granted it first.
+		.onDuplicateKeyUpdate({role})
+		.execute();
+};
+
+/** Disabling revokes every session: a disabled user must lose access now, not
+ *  when their 30-day cookie happens to expire. */
+export const disableUser = async (userId: string): Promise<void> => {
+	await db.transaction().execute(async trx => {
+		await trx.updateTable('user').set({disabled: true}).where('id', '=', userId).execute();
+		await trx.deleteFrom('session').where('userId', '=', userId).execute();
+	});
+};
+
+export const enableUser = async (userId: string): Promise<void> => {
+	await db.updateTable('user').set({disabled: false}).where('id', '=', userId).execute();
+};
+
+export const revokeSession = async (userId: string, sessionId: string): Promise<boolean> => {
+	const result = await db
+		.deleteFrom('session')
+		.where('id', '=', sessionId)
+		.where('userId', '=', userId)
+		.executeTakeFirst();
+
+	return Number(result.numDeletedRows) > 0;
+};
+
+/**
+ * Guard input for the self-lockout rules: how many enabled users still hold the
+ * `admin` permission. Disabled admins do not count - they cannot sign in, so
+ * leaving only disabled admins is the same lockout as leaving none.
+ */
+export const countActiveAdmins = async (): Promise<number> => {
+	const row = await db
+		.selectFrom('user_app_permissions')
+		.innerJoin('user', 'user.id', 'user_app_permissions.user_id')
+		.where('user_app_permissions.app', '=', 'admin')
+		.where('user.disabled', '=', false)
+		.select(({fn}) => fn.countAll<number>().as('count'))
+		.executeTakeFirst();
+
+	return Number(row?.count ?? 0);
+};
+
+export const userExists = async (userId: string): Promise<boolean> => {
+	const row = await db.selectFrom('user').select('id').where('id', '=', userId).executeTakeFirst();
+	return Boolean(row);
+};
+
+export const findUserByEmail = async (email: string): Promise<{id: string; email: string} | null> => {
+	const row = await db
+		.selectFrom('user')
+		.select(['id', 'email'])
+		.where('email', '=', email)
+		.executeTakeFirst();
+
+	return row ?? null;
+};