UserMFASettingList field of AdminGetUserResponse is empty

I need to determine the MFA configuration for a specific Cognito user via SDK.

My current logic is based on AdminGetUser API and in particular on userMFASettingList and preferredMfaSetting response fields.

As per https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/clients/client-cognito-identity-provider/modules/admingetuserresponse.html#usermfasettinglist, userMFASettingList is defined as

The MFA options that are activated for the user. The possible values in this list are SMS_MFA and SOFTWARE_TOKEN_MFA.

while mfaOptions is marked as deprecated and its use is discouraged.

I tested a pool with mandatory SMS MFA but userMFASettingList is empty, despite being able to complete the MFA challenge and log in successfully via Cognito Hosted UI.

Is this a bug? What logic should I use?

Is this a bug?

Seems like it.

Unless you call AdminSetUserMFAPreference at least once, UserMFASettingList will always be empty by default in a AdminGetUser call even if MFAOptions is correctly populated.

This is not returned / empty at an API level, so the SDK doesn't make a difference here.

1. Create user
2. Go through setting up MFA
3. Note that console says 'MFA methods: SMS'
4. Call AdminGetUser and check that UserMFASettingList is empty while MFAOptions is populated
5. Call AdminSetUserMFAPreference to 'reassert' the SMS MFA option
6. Call AdminGetUser again and check that both UserMFASettingList & MFAOptions are now populated, even though you practically didn't change anything

➜  ~ aws cognito-idp admin-get-user \
     --region eu-west-1 \
     --user-pool-id xxx \
     --username user1 \
     | jq .

{
  "Username": "user1",
  "UserAttributes": [
    ...
  ],
  "UserCreateDate": "xxx",
  "UserLastModifiedDate": "xxx",
  "Enabled": true,
  "UserStatus": "CONFIRMED",
  "MFAOptions": [
    {
      "DeliveryMedium": "SMS",
      "AttributeName": "phone_number"
    }
  ]
}

➜  ~ aws cognito-idp admin-set-user-mfa-preference \
    --user-pool-id xxx \
    --username user1 \
    --sms-mfa-settings Enabled=true

➜  ~ aws cognito-idp admin-get-user \
     --region eu-west-1 \
     --user-pool-id xxx \
     --username user1 \
     | jq .

{
  "Username": "user1",
  "UserAttributes": [
    ...
  ],
  "UserCreateDate": "xxx",
  "UserLastModifiedDate": "xxx",
  "Enabled": true,
  "UserStatus": "CONFIRMED",
  "MFAOptions": [
    {
      "DeliveryMedium": "SMS",
      "AttributeName": "phone_number"
    }
  ],
  "UserMFASettingList": [
    "SMS_MFA"
  ]
}

I need to determine the MFA configuration for a specific Cognito user via SDK.

What logic should I use?

Sadly, you can't easily do it.

You need a combination of PreferredMfaSetting & UserMFASettingList to be able to determine the MFA configuration for a user. With the above bug (as far as I can see) fixed, even if UserMFASettingList is populated correctly first time round, that's just a list of available MFA options for the user. It's not what the user has selected.

There isn't a CurrentMfaSetting field returned by the Cognito API.