feat(ldap): encrypt the bind password at rest

The LDAP bind password was the only credential still stored in clear text.
CalendarSource, SmtpConfig, DkvModuleConfig and TenderEmailConfig have been
AES-256-GCM encrypted for a while; LDAP simply predated the encryption service
and was never brought along.

Hashing is not an option here: Tessera has to replay this password to bind
against the directory, so it must stay recoverable. Encryption at rest covers
the case a hash cannot help with either way -- a database dump or backup
leaving the host without the key, which lives in the application environment.
It does not protect against a compromised host, and does not pretend to.

Reuses CalendarCryptoService, the same provider SettingsModule, DkvModule and
TendersModule already inject, rather than introducing a second crypto path.
The name is a historical accident and is noted as such in LdapModule; renaming
it touches five modules and belongs in its own change.

Decryption sits in getConfig()/getAllActiveConfigs(), the two methods every
consumer already goes through, so callers keep reading a plain `bindPassword`
and the controller keeps masking it to '********' in responses.

The migration only renames the column -- SQL cannot encrypt, since the key is
not in the database. An idempotent bootstrap backfill encrypts rows written
before this change, and until it has run the read path passes a legacy
plaintext value through unchanged so the sync does not break in that window.
A failed decrypt throws rather than returning null: a wrong key must not read
as "no password configured" and silently turn an authenticated bind into an
anonymous one.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

apps/api/src/ldap/ldap-config.service.ts

@@ -1,4 +1,5 @@
-import { Injectable } from '@nestjs/common';
+import { Injectable, Logger, OnApplicationBootstrap } from '@nestjs/common';
+import { CalendarCryptoService } from '../calendar/crypto.service';
 import { PrismaService } from '../prisma/prisma.service';
 import {
   CreateFieldMappingDto,
@@ -6,22 +7,125 @@ import {
   UpdateLdapConfigDto,
 } from './dto/ldap-config.dto';
 
+/**
+ * Shape of a stored AES-256-GCM value as CalendarCryptoService writes it:
+ * `iv:authTag:ciphertext`, all hex. Used to tell an encrypted value apart from
+ * a legacy plaintext one that predates the encryption of this column.
+ */
+const ENCRYPTED_VALUE_SHAPE = /^[0-9a-f]+:[0-9a-f]+:[0-9a-f]*$/i;
+
 /**
  * Per-tenant LDAP configuration CRUD (D-18).
  * Manages LDAP connection settings and field mappings.
+ *
+ * The bind password is stored AES-256-GCM-encrypted in
+ * `LdapConfig.encryptedBindPassword`, the same way CalendarSource, SmtpConfig,
+ * DkvModuleConfig and TenderEmailConfig store theirs. It cannot be hashed:
+ * Tessera has to replay this password to bind against the directory, so it
+ * needs to be recoverable. Encryption at rest protects the one case a hash
+ * cannot help with anyway — a database dump or backup leaving the host without
+ * the key that lives in the application environment.
+ *
+ * Every consumer reads the config through `getConfig()` or
+ * `getAllActiveConfigs()`, so decryption happens in exactly those two places
+ * and callers keep seeing a plain `bindPassword` field. The controller still
+ * masks it to '********' in API responses (T-02-17).
  */
 @Injectable()
-export class LdapConfigService {
-  constructor(private prisma: PrismaService) {}
+export class LdapConfigService implements OnApplicationBootstrap {
+  private readonly logger = new Logger(LdapConfigService.name);
+
+  constructor(
+    private prisma: PrismaService,
+    private readonly crypto: CalendarCryptoService,
+  ) {}
+
+  /**
+   * One-time, idempotent backfill of rows written before this column was
+   * encrypted. SQL cannot do this — the key lives in the application
+   * environment, not in the database — so the migration only renames the
+   * column and the actual encryption happens here on the next start.
+   *
+   * Runs on every boot and is a no-op once every row is encrypted. A failure
+   * is logged and swallowed: a tenant whose bind password could not be
+   * re-encrypted still authenticates, because the read path below tolerates a
+   * legacy plaintext value.
+   */
+  async onApplicationBootstrap(): Promise<void> {
+    try {
+      const configs = await this.prisma.ldapConfig.findMany({
+        select: { id: true, tenantId: true, encryptedBindPassword: true },
+      });
+
+      const legacy = configs.filter(
+        (config) =>
+          config.encryptedBindPassword &&
+          !ENCRYPTED_VALUE_SHAPE.test(config.encryptedBindPassword),
+      );
+      if (legacy.length === 0) return;
+
+      for (const config of legacy) {
+        await this.prisma.ldapConfig.update({
+          where: { id: config.id },
+          data: {
+            encryptedBindPassword: this.crypto.encrypt(
+              config.encryptedBindPassword as string,
+            ),
+          },
+        });
+      }
+
+      this.logger.log(
+        `LDAP-Bind-Passwort verschluesselt: ${legacy.length} Konfiguration(en) nachgezogen`,
+      );
+    } catch (err) {
+      this.logger.error(
+        `Backfill der LDAP-Bind-Passwoerter fehlgeschlagen: ${(err as Error).message}`,
+      );
+    }
+  }
+
+  /**
+   * Decrypt for internal use. A value that is not in `iv:authTag:ciphertext`
+   * form predates the encryption and is returned unchanged — that window
+   * exists between the column rename and the bootstrap backfill above, and
+   * must not break the sync.
+   */
+  private decryptBindPassword(stored: string | null): string | null {
+    if (!stored) return null;
+    if (!ENCRYPTED_VALUE_SHAPE.test(stored)) return stored;
+    try {
+      return this.crypto.decrypt(stored);
+    } catch (err) {
+      // A wrong or rotated key must not read as "no password configured" —
+      // that would silently turn an authenticated bind into an anonymous one.
+      this.logger.error(
+        `LDAP-Bind-Passwort konnte nicht entschluesselt werden (falscher CALENDAR_ENCRYPTION_KEY?): ${(err as Error).message}`,
+      );
+      throw err;
+    }
+  }
+
+  /** Map a stored row to what callers expect: a plain `bindPassword` field. */
+  private withDecryptedPassword<
+    T extends { encryptedBindPassword: string | null },
+  >(config: T): Omit<T, 'encryptedBindPassword'> & { bindPassword: string | null } {
+    const { encryptedBindPassword, ...rest } = config;
+    return {
+      ...rest,
+      bindPassword: this.decryptBindPassword(encryptedBindPassword),
+    };
+  }
 
   /**
    * Get LDAP config for a tenant, including field mappings.
    */
   async getConfig(tenantId: string) {
-    return this.prisma.ldapConfig.findUnique({
+    const config = await this.prisma.ldapConfig.findUnique({
       where: { tenantId },
       include: { fieldMappings: true },
     });
+    return config ? this.withDecryptedPassword(config) : null;
   }
 
   /**
@@ -29,13 +133,15 @@ export class LdapConfigService {
    * Defaults: displayName -> displayName, mail -> email, sAMAccountName -> username
    */
   async createConfig(tenantId: string, dto: CreateLdapConfigDto) {
-    return this.prisma.ldapConfig.create({
+    const created = await this.prisma.ldapConfig.create({
       data: {
         tenantId,
         serverUrl: dto.serverUrl,
         baseDn: dto.baseDn,
         bindDn: dto.bindDn,
-        bindPassword: dto.bindPassword,
+        encryptedBindPassword: dto.bindPassword
+          ? this.crypto.encrypt(dto.bindPassword)
+          : null,
         searchFilter: dto.searchFilter ?? '(objectClass=person)',
         syncIntervalMin: dto.syncIntervalMin ?? 60,
         isActive: dto.isActive ?? true,
@@ -60,20 +166,24 @@ export class LdapConfigService {
       },
       include: { fieldMappings: true },
     });
+    return this.withDecryptedPassword(created);
   }
 
   /**
    * Update LDAP config for a tenant.
    */
   async updateConfig(tenantId: string, dto: UpdateLdapConfigDto) {
-    return this.prisma.ldapConfig.update({
+    const updated = await this.prisma.ldapConfig.update({
       where: { tenantId },
       data: {
         ...(dto.serverUrl !== undefined && { serverUrl: dto.serverUrl }),
         ...(dto.baseDn !== undefined && { baseDn: dto.baseDn }),
         ...(dto.bindDn !== undefined && { bindDn: dto.bindDn }),
+        // An empty string means "clear the password", not "encrypt nothing".
         ...(dto.bindPassword !== undefined && {
-          bindPassword: dto.bindPassword,
+          encryptedBindPassword: dto.bindPassword
+            ? this.crypto.encrypt(dto.bindPassword)
+            : null,
         }),
         ...(dto.searchFilter !== undefined && {
           searchFilter: dto.searchFilter,
@@ -94,6 +204,7 @@ export class LdapConfigService {
       },
       include: { fieldMappings: true },
     });
+    return this.withDecryptedPassword(updated);
   }
 
   /**
@@ -137,9 +248,10 @@ export class LdapConfigService {
    * tenants need auto-sync.
    */
   async getAllActiveConfigs() {
-    return this.prisma.ldapConfig.findMany({
+    const configs = await this.prisma.ldapConfig.findMany({
       where: { isActive: true },
       include: { tenant: true, fieldMappings: true },
     });
+    return configs.map((config) => this.withDecryptedPassword(config));
   }
 }