Multi-factor authentication

Amplify Auth supports multi-factor authentication (MFA) for user sign-in flows. MFA is an extra layer of security used to make sure that users trying to gain access to an account are who they say they are. It requires users to provide additional information to verify their identity. Amplify Auth supports MFA with time-based one-time passwords (TOTP), text messages (SMS), and email.

In this guide we will review how you can set up MFA with each of these methods and the discuss tradeoffs between them to help you choose the right setup for your application. We will also review how to set up MFA to remember a device and reduce sign-in friction for your users.

Configure multi-factor authentication

Use defineAuth to enable MFA for your app. The example below is setting up MFA with TOTP but not SMS as you can see that the phone number is not a required attribute.

• If you plan to use SMS for MFA, then the phoneNumber attribute must be marked as required in your userAttributes. Note that if you have loginWith.phone as true this attribute will automatically be marked as required.
• If you plan to use email for MFA, then the email attribute must also be true must be marked as required in your userAttributes. Note that if you have loginWith.email as true this attribute will automatically be marked as required.

import { defineAuth } from '@aws-amplify/backend';

export const auth = defineAuth({
  loginWith: {
    email: true
  },
Copy highlighted code example
  multifactor: {
    mode: 'OPTIONAL',
    totp: true,
  },
  userAttributes: {
    phoneNumber: { 
      required: true
    }
  }
});

When MFA is REQUIRED with SMS in your backend auth resource, you will need to pass the phone number during sign-up API call. If you are using the email or username as the primary sign-in mechanism, you will need to pass the phone_number attribute as a user attribute.

Similarly, when MFA is REQUIRED with email as your delivery mechanism, you will need to pass an email address during the sign-up API call. If you are using phoneNumber or username as the primary sign-in mechanism, you will need to pass the email attribute as a user attribute.

This configuration may change depending on the combination of MFA methods enabled in your user pool.

Understand your MFA options

When enabling MFA you will have two key decisions to make:

• MFA enforcement: As part of this setup you will determine how MFA is enforced. If you require MFA by setting MFA mode to REQUIRED, all your users will need to complete MFA to sign in. If you keep it OPTIONAL, your users will have the choice whether to enable MFA or not for their account.
• MFA methods: You will also specify which MFA method you are using: TOTP (Time-based One-time Password), SMS (text message), email, or any combination thereof. We recommend that you use TOTP-based MFA as it is more secure and you can reserve SMS or email for account recovery.

If multiple MFA methods are enabled for the user, and none are set as preferred, the signIn API will return continueSignInWithMFASelection as the next step in the auth flow. During this scenario, the user should be prompted to select the MFA method they want to use to sign in and their preference should be passed to confirmSignIn.

Future<void> _handleSignInResult(SignInResult result) async {
  switch (result.nextStep.signInStep) {
    // ···
    case AuthSignInStep.continueSignInWithMfaSelection:
      final allowedMfaTypes = result.nextStep.allowedMfaTypes!;
      final selection = await _promptUserPreference(allowedMfaTypes);
      return _handleMfaSelection(selection);
    // ···
  }
}

Future<MfaType> _promptUserPreference(Set<MfaType> allowedTypes) async {
  // ···
}

Future<void> _handleMfaSelection(MfaType selection) async {
  try {
    final result = await Amplify.Auth.confirmSignIn(
      confirmationValue: selection.confirmationValue,
    );
    return _handleSignInResult(result);
  } on AuthException catch (e) {
    safePrint('Error sending MFA selection: ${e.message}');
  }
}

Multi-factor authentication with SMS

Once you have setup SMS as your second layer of authentication with MFA as shown above, your users will get an authentication code via a text message to complete sign-in after they sign in with their username and password.

Enable SMS MFA during sign-up

You will need to pass phone_number as a user attribute to enable SMS MFA for your users during sign-up. However, if the primary sign-in mechanism for your Cognito resource is phone_number (without enabling username), then you do not need to pass it as an attribute.

Future<void> signUpWithPhoneVerification(
  String username,
  String password,
) async {
  await Amplify.Auth.signUp(
    username: username,
    password: password,
    options: SignUpOptions(
      userAttributes: <AuthUserAttributeKey, String>{
        // ... if required
        AuthUserAttributeKey.email: 'test@example.com',
        AuthUserAttributeKey.phoneNumber: '+18885551234',
      },
    ),
  );
}

By default, you have to verify a user account after they sign up using the confirmSignUp API, which will send a one-time password to the user's phone number or email, depending on your Amazon Cognito configuration.

Future<void> confirmSignUpPhoneVerification(
  String username,
  String otpCode,
) async {
  await Amplify.Auth.confirmSignUp(
    username: username,
    confirmationCode: otpCode,
  );
}

Manage SMS MFA during sign-in

After a user signs in, if they have MFA enabled for their account, a challenge will be returned that you would need to call the confirmSignIn API where the user provides their confirmation code sent to their phone number.

If MFA is ON or enabled for the user, you must call confirmSignIn with the OTP sent to their phone.

Future<void> confirmSignInPhoneVerification(String otpCode) async {
  await Amplify.Auth.confirmSignIn(
    confirmationValue: otpCode,
  );
}

After a user has been signed in, call updateMFAPreference to record the MFA type as enabled for the user and optionally set it as preferred so that subsequent logins default to using this MFA type.

Future<void> updateMfaPreferences() async {
  final cognitoPlugin = Amplify.Auth.getPlugin(AmplifyAuthCognito.pluginKey);

  await cognitoPlugin.updateMfaPreference(
    sms: MfaPreference.enabled, // or .preferred
  );
}

Multi-factor authentication with TOTP

You can use Time-based One-Time Password (TOTP) for multi-factor authentication (MFA) in your web or mobile applications. The Amplify Auth category includes support for TOTP setup and verification using authenticator apps, offering an integrated solution and enhanced security for your users. These apps, such as Google Authenticator, Microsoft Authenticator, have the TOTP algorithm built-in and work by using a shared secret key and the current time to generate short-lived, six digit passwords.

Set up TOTP for a user

After you initiate a user sign in with the signIn API where a user is required to set up TOTP as an MFA method, the API call will return continueSignInWithTOTPSetup as a challenge and next step to handle in your app. You will get that challenge if the following conditions are met:

• MFA is marked as Required in your user pool.
• TOTP is enabled in your user pool.
• User does not have TOTP MFA set up already.

The continueSignInWithTOTPSetup step signifies that the user must set up TOTP before they can sign in. The step returns an associated value of type TOTPSetupDetails which must be used to configure an authenticator app like Microsoft Authenticator or Google Authenticator. TOTPSetupDetails provides a helper method called getSetupURI which generates a URI that can be used, for example, in a button to open the user's installed authenticator app. For more advanced use cases, TOTPSetupDetails also contains a sharedSecret which can be used to either generate a QR code or be manually entered into an authenticator app.

Once the authenticator app is set up, the user can generate a TOTP code and provide it to the library to complete the sign in process.

Future<void> signInUser(String username, String password) async {
  try {
    final result = await Amplify.Auth.signIn(
      username: username,
      password: password,
    );
    return _handleSignInResult(result);
  } on AuthException catch (e) {
    safePrint('Error signing in: ${e.message}');
  }
}

Future<void> _handleSignInResult(SignInResult result) async {
  switch (result.nextStep.signInStep) {
    // ···
    case AuthSignInStep.continueSignInWithTotpSetup:
      final totpSetupDetails = result.nextStep.totpSetupDetails!;
      final setupUri = totpSetupDetails.getSetupUri(appName: 'MyApp');
      safePrint('Open URI to complete setup: $setupUri');
    // ···
  }
}

The TOTP code can be obtained from the user via a text field or any other means. Once the user provides the TOTP code, call confirmSignIn with the TOTP code as the challengeResponse parameter.

Future<void> confirmTotpUser(String totpCode) async {
  try {
    final result = await Amplify.Auth.confirmSignIn(
      confirmationValue: totpCode,
    );
    return _handleSignInResult(result);
  } on AuthException catch (e) {
    safePrint('Error confirming TOTP code: ${e.message}');
  }
}

After a user has been signed in, call updateMFAPreference to record the MFA type as enabled for the user and optionally set it as preferred so that subsequent logins default to using this MFA type.

Future<void> updateMfaPreferences() async {
  final cognitoPlugin = Amplify.Auth.getPlugin(AmplifyAuthCognito.pluginKey);

  await cognitoPlugin.updateMfaPreference(
    totp: MfaPreference.preferred,
  );
}

Enable TOTP after a user is signed in

TOTP MFA can be set up after a user has signed in. This can be done when the following conditions are met:

• MFA is marked as Optional or Required in your user pool.
• TOTP is marked as an enabled MFA method in your user pool.

TOTP can be set up by calling the setUpTOTP and verifyTOTPSetup APIs in the Auth category.

Invoke the setUpTOTP API to generate a TOTPSetupDetails object which should be used to configure an Authenticator app like Microsoft Authenticator or Google Authenticator. TOTPSetupDetails provides a helper method called getSetupURI which generates a URI that can be used, for example, in a button to open the user's installed Authenticator app. For more advanced use cases, TOTPSetupDetails also contains a sharedSecret which can be used to either generate a QR code or be manually entered into an Authenticator app.

that contains the sharedSecret which will be used to either to generate a QR code or can be manually entered into an Authenticator app.

Future<void> setUpTotp() async {
  try {
    final totpSetupDetails = await Amplify.Auth.setUpTotp();
    final setupUri = totpSetupDetails.getSetupUri(appName: 'MyApp');
    safePrint('Open URI to complete setup: $setupUri');
  } on AuthException catch (e) {
    safePrint('An error occurred setting up TOTP: $e');
  }
}

Once the Authenticator app is set up, the user must generate a TOTP code and provide it to the library. Pass the code to verifyTOTPSetup to complete the TOTP setup process.

Future<void> verifyTotpSetup(String totpCode) async {
  try {
    await Amplify.Auth.verifyTotpSetup(totpCode);
  } on AuthException catch (e) {
    safePrint('An error occurred verifying TOTP: $e');
  }
}

After TOTP setup is complete, call updateMFAPreference to record the MFA type as enabled for the user and optionally set it as preferred so that subsequent logins default to using this MFA type.

Future<void> updateMfaPreferences() async {
  final cognitoPlugin = Amplify.Auth.getPlugin(AmplifyAuthCognito.pluginKey);

  await cognitoPlugin.updateMfaPreference(
    sms: MfaPreference.enabled,
    totp: MfaPreference.preferred,
  );
}

Recover from a lost TOTP device

In a scenario where MFA is marked as "Required" in the Cognito User Pool and another MFA method is not set up, the administrator would need to first initiate an AdminUpdateUserAttributes call and update the user's phone number attribute. Once this is complete, the administrator can continue changing the MFA preference to SMS as suggested above.

Multi-factor authentication with EMAIL

Once you have setup email as your second layer of authentication with MFA as shown above, your users will get an authentication code via email to complete sign-in after they sign in with their username and password.

Enable EMAIL MFA during sign-up

You will need to pass email as a user attribute to enable email MFA for your users during sign-up. However, if the primary sign-in mechanism for your Cognito resource is already email (without enabling username), then you do not need to pass it as an attribute.

Future<void> signUpWithEmailVerification(
  String username,
  String password,
) async {
  await Amplify.Auth.signUp(
    username: username,
    password: password,
    options: SignUpOptions(
      userAttributes: <AuthUserAttributeKey, String>{
        AuthUserAttributeKey.email: 'test@example.com',
        // ... if required
        AuthUserAttributeKey.phoneNumber: '+18885551234',
      },
    ),
  );
}

By default, you have to verify a user account after they sign up using the confirmSignUp API. Following the initial signUp request, a one-time passcode will be sent to the user's phone number or email, depending on your Amazon Cognito configuration.

Future<void> confirmSignUpEmailVerification(
  String username,
  String otpCode,
) async {
  await Amplify.Auth.confirmSignUp(
    username: username,
    confirmationCode: otpCode,
  );
}

Manage EMAIL MFA during sign-in

After a user signs in, if they have MFA enabled for their account, a challenge will be issued that requires calling the confirmSignIn API with the user provided confirmation code sent to their email address.

If MFA is ON or enabled for the user, you must call confirmSignIn with the OTP sent to their email address.

Future<void> confirmSignInEmailVerification(String otpCode) async {
  await Amplify.Auth.confirmSignIn(
    confirmationValue: otpCode,
  );
}

After a user has been signed in, call updateMFAPreference to record the MFA type as enabled for the user and optionally set it as preferred so that subsequent logins default to using this MFA type.

Future<void> updateMfaPreferences() async {
  final cognitoPlugin = Amplify.Auth.getPlugin(AmplifyAuthCognito.pluginKey);

  await cognitoPlugin.updateMfaPreference(
    email: MfaPreference.enabled, // or .preferred
  );
}

Set up a user's preferred MFA method

Depending on your user pool configuration, it's possible that multiple MFA options may be available to a given user. In order to avoid requiring your users to select an MFA method each time they sign-in to your application, Amplify provides two utility APIs to manage an individual user's MFA preferences.

Fetch the current user's MFA preferences

Invoke the following API to get the current MFA preference and enabled MFA types, if any, for the current user.

Future<void> getCurrentMfaPreference() async {
  final cognitoPlugin = Amplify.Auth.getPlugin(AmplifyAuthCognito.pluginKey);

  final currentPreference = await cognitoPlugin.fetchMfaPreference();
  safePrint('Enabled MFA types for user: ${currentPreference.enabled}');
  safePrint('Preferred MFA type for user: ${currentPreference.preferred}');
}

Update the current user's MFA preferences

Invoke the following API to update the MFA preference for the current user.

Future<void> updateMfaPreferences() async {
  final cognitoPlugin = Amplify.Auth.getPlugin(AmplifyAuthCognito.pluginKey);

  await cognitoPlugin.updateMfaPreference(
    sms: MfaPreference.enabled,
    totp: MfaPreference.preferred,
  );
}

Remember a device

Remembering a device is useful in conjunction with MFA because it allows the second factor requirement to be automatically met when your user signs in on that device and reduces friction in their sign-in experience. By default, this feature is turned off.

Configure device tracking

You can configure device tracking with deviceTracking construct.

import { defineBackend } from '@aws-amplify/backend';
import { auth } from './auth/resource';
import { data } from './data/resource';

const backend = defineBackend({
  auth,
  data
});

const { cfnUserPool } = backend.auth.resources.cfnResources;

cfnUserPool.addPropertyOverride('DeviceConfiguration', {
  ChallengeRequiredOnNewDevice: true,
  DeviceOnlyRememberedOnUserPrompt: false
});

Next steps

• Learn how to sign-up with MFA enabled
• Learn how to manage user devices