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 the MFA methods with Time-based-One-Time Passwords (TOTP) as well as text messages (SMS). In this guide we will review how you can set up MFA using TOTP and SMS and the tradeoffs between these methods to help you choose the right set up 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 are using SMS, then the PhoneNumber attribute must be true.

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

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

When multi-factor authentication (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. This will change depending on if you enable SMS, TOTP, or both. Visit the multi-factor authentication documentation to learn more about enabling MFA on your backend auth resource.

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 login to "ON", 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), or both. We recommend that you use TOTP-based MFA as it is more secure and you can reserve SMS for account recovery.

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.

import { signUp } from 'aws-amplify/auth';

await signUp({
  username: "hello@mycompany.com",
  password: "hunter2",
  options: {
    userAttributes: {
      phone_number: "+15555555555",
      email: "hello@mycompany.com",
    },
  },
});

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.

import { confirmSignUp } from 'aws-amplify/auth';

await confirmSignUp({
  username: "hello@mycompany.com",
  confirmationCode: "123456",
})

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.

import { confirmSignIn } from 'aws-amplify/auth';

await confirmSignIn({
  challengeResponse: "123456"
});

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.

import { updateMFAPreference } from 'aws-amplify/auth';

await updateMFAPreference({ sms: '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 CONTINUE_SIGN_IN_WITH_TOTP_SETUP 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 CONTINUE_SIGN_IN_WITH_TOTP_SETUP 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.

import { signIn, SignInOutput } from 'aws-amplify/auth';

const output = await signIn({
  username: "hello@mycompany.com",
  password: "hunter2"
});

const { nextStep } = output;
switch (nextStep.signInStep) {
  // ...
  case 'CONTINUE_SIGN_IN_WITH_TOTP_SETUP':
    const totpSetupDetails = nextStep.totpSetupDetails;
    const appName = 'my_app_name';
    const setupUri = totpSetupDetails.getSetupUri(appName);
    // Open setupUri with an authenticator APP to retrieve an OTP code
    break;
  // ...
}

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.

import { confirmSignIn } from 'aws-amplify/auth';

await confirmSignIn({
  challengeResponse: "123456"
});

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.

import { updateMFAPreference } from 'aws-amplify/auth';

await updateMFAPreference({ totp: '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.

import { setUpTOTP } from 'aws-amplify/auth';

const totpSetupDetails = await setUpTOTP();
const appName = 'my_app_name';
const setupUri = totpSetupDetails.getSetupUri(appName);
// Open setupUri with an authenticator APP to retrieve an OTP code

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.

import { verifyTOTPSetup } from 'aws-amplify/auth';

await verifyTOTPSetup({ code: "123456" });

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.

import { updateMFAPreference } from 'aws-amplify/auth';

await updateMFAPreference({ sms: 'ENABLED', totp: '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.

Set up a user's preferred MFA method

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.

import { fetchMFAPreference } from 'aws-amplify/auth';

const { enabled, preferred } = await fetchMFAPreference();

Update the current user's MFA preferences

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

import { updateMFAPreference } from 'aws-amplify/auth';

await updateMFAPreference({ sms: 'ENABLED', totp: 'PREFERRED' });

If multiple MFA methods are enabled for the user, the signIn API will return CONTINUE_SIGN_IN_WITH_MFA_SELECTION 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.

import { confirmSignIn, SignInOutput } from 'aws-amplify/auth';

function handleSignInNextSteps(output: SignInOutput) {
  const { nextStep } = output;
  switch (nextStep.signInStep) {
    // ...
    case 'CONTINUE_SIGN_IN_WITH_MFA_SELECTION':
      const allowedMFATypes = nextStep.allowedMFATypes;
      const mfaType = promptUserForMFAType(allowedMFATypes);
    case 'CONFIRM_SIGN_IN_WITH_SMS_CODE':
      // display user to enter otp code;
      break;
    case 'CONFIRM_SIGN_IN_WITH_TOTP_CODE':
      // display user to enter otp code;
      break;
    // ...
  }
}

function promptUserForMFAType(
  allowedMFATypes?: ('SMS' | 'TOTP')[]
): 'SMS' | 'TOTP' {
  // Prompt user to select MFA type
}

async function handleMFASelection(mfaType: 'SMS' | 'TOTP') {
  try {
    const output = await confirmSignIn({
      challengeResponse: mfaType
    });
    handleSignInNextSteps(output);
  } catch (error) {
    console.log(error);
  }
}

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