feat: SaaS onboarding, Stripe billing, MFA, SSO, passkeys, refresh tokens

Complete SaaS self-service onboarding sprint:

- Stripe-powered signup flow: pricing page → checkout → provisioning → activation
- Refresh token infrastructure: 1h access tokens + 30-day httpOnly cookie refresh
- TOTP MFA with QR setup, recovery codes, and login challenge flow
- Google + Azure AD SSO (conditional on env vars) with account linking
- WebAuthn passkey registration and passwordless login
- Guided onboarding checklist with server-side progress tracking
- Stubbed email service (console + DB logging, ready for real provider)
- Settings page with tabbed security settings (MFA, passkeys, linked accounts)
- Login page enhanced with MFA verification, SSO buttons, passkey login
- Database migration 015 with all new tables and columns
- Version bump to 2026.03.17

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

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

@@ -0,0 +1,97 @@
+import { Injectable, Logger, BadRequestException } from '@nestjs/common';
+import { DataSource } from 'typeorm';
+import { UsersService } from '../users/users.service';
+
+interface SsoProfile {
+  provider: string;
+  providerId: string;
+  email: string;
+  firstName?: string;
+  lastName?: string;
+}
+
+@Injectable()
+export class SsoService {
+  private readonly logger = new Logger(SsoService.name);
+
+  constructor(
+    private dataSource: DataSource,
+    private usersService: UsersService,
+  ) {}
+
+  /**
+   * Find existing user by SSO provider+id, or by email match, or create new.
+   */
+  async findOrCreateSsoUser(profile: SsoProfile) {
+    // 1. Try to find by provider + provider ID
+    const byProvider = await this.dataSource.query(
+      `SELECT * FROM shared.users WHERE oauth_provider = $1 AND oauth_provider_id = $2`,
+      [profile.provider, profile.providerId],
+    );
+    if (byProvider.length > 0) {
+      return this.usersService.findByIdWithOrgs(byProvider[0].id);
+    }
+
+    // 2. Try to find by email match (link accounts)
+    const byEmail = await this.usersService.findByEmail(profile.email);
+    if (byEmail) {
+      // Link the SSO provider to existing account
+      await this.linkSsoAccount(byEmail.id, profile.provider, profile.providerId);
+      return this.usersService.findByIdWithOrgs(byEmail.id);
+    }
+
+    // 3. Create new user
+    const newUser = await this.dataSource.query(
+      `INSERT INTO shared.users (email, first_name, last_name, oauth_provider, oauth_provider_id, is_email_verified)
+       VALUES ($1, $2, $3, $4, $5, true)
+       RETURNING id`,
+      [profile.email, profile.firstName || '', profile.lastName || '', profile.provider, profile.providerId],
+    );
+
+    return this.usersService.findByIdWithOrgs(newUser[0].id);
+  }
+
+  /**
+   * Link an SSO provider to an existing user.
+   */
+  async linkSsoAccount(userId: string, provider: string, providerId: string): Promise<void> {
+    await this.dataSource.query(
+      `UPDATE shared.users SET oauth_provider = $1, oauth_provider_id = $2, updated_at = NOW() WHERE id = $3`,
+      [provider, providerId, userId],
+    );
+    this.logger.log(`Linked ${provider} SSO to user ${userId}`);
+  }
+
+  /**
+   * Unlink SSO from a user (only if they have a password set).
+   */
+  async unlinkSsoAccount(userId: string, provider: string): Promise<void> {
+    const rows = await this.dataSource.query(
+      `SELECT password_hash, oauth_provider FROM shared.users WHERE id = $1`,
+      [userId],
+    );
+    if (rows.length === 0) throw new BadRequestException('User not found');
+    if (!rows[0].password_hash) {
+      throw new BadRequestException('Cannot unlink SSO — you must set a password first');
+    }
+    if (rows[0].oauth_provider !== provider) {
+      throw new BadRequestException('SSO provider mismatch');
+    }
+
+    await this.dataSource.query(
+      `UPDATE shared.users SET oauth_provider = NULL, oauth_provider_id = NULL, updated_at = NOW() WHERE id = $1`,
+      [userId],
+    );
+    this.logger.log(`Unlinked ${provider} SSO from user ${userId}`);
+  }
+
+  /**
+   * Get which SSO providers are configured.
+   */
+  getAvailableProviders(): { google: boolean; azure: boolean } {
+    return {
+      google: !!(process.env.GOOGLE_CLIENT_ID && process.env.GOOGLE_CLIENT_SECRET),
+      azure: !!(process.env.AZURE_CLIENT_ID && process.env.AZURE_CLIENT_SECRET),
+    };
+  }
+}