Add Optional 2FA Support (#61)

* Add TOTP MFA Support

* Add Passkey MFA Support

It's not impossible I missed some minor cleanup, but most things make sense and there isn't a lot of obvious duplication anymore.

---------

Co-authored-by: Bruno Bernardino <me@brunobernardino.com>

routes/api/auth/multi-factor/passkey/setup-begin.ts

@@ -0,0 +1,67 @@
+import { Handlers } from 'fresh/server.ts';
+import { PublicKeyCredentialCreationOptionsJSON } from '@simplewebauthn/server';
+
+import { FreshContextState } from '/lib/types.ts';
+import { AppConfig } from '/lib/config.ts';
+import { PasskeyModel } from '/lib/models/multi-factor-auth/passkey.ts';
+import { MultiFactorAuthModel } from '/lib/models/multi-factor-auth.ts';
+
+export interface RequestBody {}
+
+export interface ResponseBody {
+  success: boolean;
+  error?: string;
+  options?: PublicKeyCredentialCreationOptionsJSON;
+  sessionData?: {
+    challenge: string;
+    methodId: string;
+    userId: string;
+  };
+}
+
+export const handler: Handlers<unknown, FreshContextState> = {
+  async POST(request, context) {
+    if (!context.state.user) {
+      return new Response('Unauthorized', { status: 401 });
+    }
+
+    const isMultiFactorAuthEnabled = await AppConfig.isMultiFactorAuthEnabled();
+
+    if (!isMultiFactorAuthEnabled) {
+      const responseBody: ResponseBody = {
+        success: false,
+        error: 'Passwordless passkey login requires multi-factor authentication to be enabled.',
+      };
+
+      return new Response(JSON.stringify(responseBody), { status: 403 });
+    }
+
+    const { user } = context.state;
+
+    const methodId = MultiFactorAuthModel.generateMethodId();
+
+    const config = await AppConfig.getConfig();
+    const existingCredentials = PasskeyModel.getCredentialsFromUser(user);
+
+    const options = await PasskeyModel.generateRegistrationOptions(
+      user.id,
+      user.email,
+      config.auth.baseUrl,
+      existingCredentials,
+    );
+
+    const sessionData: ResponseBody['sessionData'] = {
+      challenge: options.challenge,
+      methodId,
+      userId: user.id,
+    };
+
+    const responseBody: ResponseBody = {
+      success: true,
+      options,
+      sessionData,
+    };
+
+    return new Response(JSON.stringify(responseBody));
+  },
+};