feat(security): address findings from v2 security assessment

- L2: Add server_tokens off to nginx configs to hide version
- M1: Add X-Frame-Options, X-Content-Type-Options, Referrer-Policy,
  Permissions-Policy headers to all nginx routes
- L3: Add global NoCacheInterceptor (Cache-Control: no-store) on all
  API responses to prevent caching of sensitive financial data
- C1: Disable open registration by default (ALLOW_OPEN_REGISTRATION env)
- H3: Add logout endpoint with correct HTTP 200 status code
- M2: Implement full password reset flow (forgot-password, reset-password,
  change-password) with hashed tokens, 15-min expiry, single-use
- Reduce JWT access token expiry from 24h to 1h
- Add EmailService stub (logs to shared.email_log)
- Add DB migration 016 for password_reset_tokens table

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/modules/auth/auth.service.ts

@@ -11,8 +11,9 @@ import { JwtService } from '@nestjs/jwt';
 import { ConfigService } from '@nestjs/config';
 import { DataSource } from 'typeorm';
 import * as bcrypt from 'bcryptjs';
-import { createHash } from 'crypto';
+import { randomBytes, createHash } from 'crypto';
 import { UsersService } from '../users/users.service';
+import { EmailService } from '../email/email.service';
 import { RegisterDto } from './dto/register.dto';
 import { User } from '../users/entities/user.entity';
 import { RefreshTokenService } from './refresh-token.service';
@@ -21,6 +22,7 @@ import { RefreshTokenService } from './refresh-token.service';
 export class AuthService {
   private readonly logger = new Logger(AuthService.name);
   private readonly inviteSecret: string;
+  private readonly appUrl: string;
 
   constructor(
     private usersService: UsersService,
@@ -28,8 +30,10 @@ export class AuthService {
     private configService: ConfigService,
     private dataSource: DataSource,
     private refreshTokenService: RefreshTokenService,
+    private emailService: EmailService,
   ) {
     this.inviteSecret = this.configService.get<string>('INVITE_TOKEN_SECRET') || 'dev-invite-secret';
+    this.appUrl = this.configService.get<string>('APP_URL') || 'http://localhost:5173';
   }
 
   async register(dto: RegisterDto) {
@@ -309,6 +313,105 @@ export class AuthService {
     return token;
   }
 
+  // ─── Password Reset Flow ──────────────────────────────────────────
+
+  /**
+   * Request a password reset. Generates a token, stores its hash, and sends an email.
+   * Silently succeeds even if the email doesn't exist (prevents enumeration).
+   */
+  async requestPasswordReset(email: string): Promise<void> {
+    const user = await this.usersService.findByEmail(email);
+    if (!user) {
+      // Silently return — don't reveal whether the account exists
+      return;
+    }
+
+    // Invalidate any existing reset tokens for this user
+    await this.dataSource.query(
+      `UPDATE shared.password_reset_tokens SET used_at = NOW()
+       WHERE user_id = $1 AND used_at IS NULL`,
+      [user.id],
+    );
+
+    // Generate a 64-byte random token
+    const rawToken = randomBytes(64).toString('base64url');
+    const tokenHash = createHash('sha256').update(rawToken).digest('hex');
+    const expiresAt = new Date(Date.now() + 15 * 60 * 1000); // 15 minutes
+
+    await this.dataSource.query(
+      `INSERT INTO shared.password_reset_tokens (user_id, token_hash, expires_at)
+       VALUES ($1, $2, $3)`,
+      [user.id, tokenHash, expiresAt],
+    );
+
+    const resetUrl = `${this.appUrl}/reset-password?token=${rawToken}`;
+    await this.emailService.sendPasswordResetEmail(user.email, resetUrl);
+  }
+
+  /**
+   * Reset password using a valid reset token.
+   */
+  async resetPassword(rawToken: string, newPassword: string): Promise<void> {
+    const tokenHash = createHash('sha256').update(rawToken).digest('hex');
+
+    const rows = await this.dataSource.query(
+      `SELECT id, user_id, expires_at, used_at
+       FROM shared.password_reset_tokens
+       WHERE token_hash = $1`,
+      [tokenHash],
+    );
+
+    if (rows.length === 0) {
+      throw new BadRequestException('Invalid or expired reset token');
+    }
+
+    const record = rows[0];
+
+    if (record.used_at) {
+      throw new BadRequestException('This reset link has already been used');
+    }
+
+    if (new Date(record.expires_at) < new Date()) {
+      throw new BadRequestException('This reset link has expired');
+    }
+
+    // Update password
+    const passwordHash = await bcrypt.hash(newPassword, 12);
+    await this.dataSource.query(
+      `UPDATE shared.users SET password_hash = $1, updated_at = NOW() WHERE id = $2`,
+      [passwordHash, record.user_id],
+    );
+
+    // Mark token as used
+    await this.dataSource.query(
+      `UPDATE shared.password_reset_tokens SET used_at = NOW() WHERE id = $1`,
+      [record.id],
+    );
+  }
+
+  /**
+   * Change password for an authenticated user (requires current password).
+   */
+  async changePassword(userId: string, currentPassword: string, newPassword: string): Promise<void> {
+    const user = await this.usersService.findById(userId);
+    if (!user || !user.passwordHash) {
+      throw new UnauthorizedException('User not found');
+    }
+
+    const isValid = await bcrypt.compare(currentPassword, user.passwordHash);
+    if (!isValid) {
+      throw new UnauthorizedException('Current password is incorrect');
+    }
+
+    const passwordHash = await bcrypt.hash(newPassword, 12);
+    await this.dataSource.query(
+      `UPDATE shared.users SET password_hash = $1, updated_at = NOW() WHERE id = $2`,
+      [passwordHash, userId],
+    );
+  }
+
+  // ─── Private Helpers ──────────────────────────────────────────────
+
   private async recordLoginHistory(
     userId: string,
     organizationId: string | null,