AppSync: Get user information in $context when using AWS_IAM auth

Question

In AppSync, when you use Cognito User Pools as your auth setting your identity you get

identity: 
   { sub: 'bcb5cd53-315a-40df-a41b-1db02a4c1bd9',
     issuer: 'https://cognito-idp.us-west-2.amazonaws.com/us-west-2_oicu812',
     username: 'skillet',
     claims: 
      { sub: 'bcb5cd53-315a-40df-a41b-1db02a4c1bd9',
        aud: '7re1oap5fhm3ngpje9r81vgpoe',
        email_verified: true,
        event_id: 'bb65ba5d-4689-11e8-bee7-2d0da8da81ab',
        token_use: 'id',
        auth_time: 1524441800,
        iss: 'https://cognito-idp.us-west-2.amazonaws.com/us-west-2_oicu812',
        'cognito:username': 'skillet',
        exp: 1524459387,
        iat: 1524455787,
        email: '[email protected]' },
     sourceIp: [ '11.222.33.200' ],
     defaultAuthStrategy: 'ALLOW',
     groups: null }

However when you use AWS_IAM auth you get

identity:
{ accountId: '12121212121', //<--- my amazon account ID
  cognitoIdentityPoolId: 'us-west-2:39b1f3e4-330e-40f6-b738-266682302b59',
  cognitoIdentityId: 'us-west-2:a458498b-b1ac-46c1-9c5e-bf932bad0d95',
  sourceIp: [ '33.222.11.200' ],
  username: 'AROAJGBZT5A433EVW6O3Q:CognitoIdentityCredentials',
  userArn: 'arn:aws:sts::454227793445:assumed-role/MEMORYCARDS-CognitoAuthorizedRole-dev/CognitoIdentityCredentials',
  cognitoIdentityAuthType: 'authenticated',
  cognitoIdentityAuthProvider: '"cognito-idp.us-west-2.amazonaws.com/us-west-2_HighBob","cognito-idp.us-west-2.amazonaws.com/us-west-2_HighBob:CognitoSignIn:1a072f08-5c61-4c89-807e-417d22702eb7"' }

The Docs says that this is expected, https://docs.aws.amazon.com/appsync/latest/devguide/resolver-context-reference.html . However, if you use AWS_IAM connected to Cognito (which is required to have unauthenticated access), how are you supposed to get at the User's username, email, sub, etc? I need access to the user's claims when using AWS_IAM type Auth.

Answer 1

For making User's username, email, sub etc. accessible through AppSync API, there's an answer for that: https://stackoverflow.com/a/42405528/1207523

To sum it up, you want to send User Pools ID token to your API (e.g. AppSync or API Gateway). Your API request is IAM authenticated. Then you validate the ID token in a Lambda function and now you have your validated IAM user and User Pools data together.

You want to use the IAM's identity.cognitoIdentityId as primary key for you User table. Add the data included in ID token (username, email, etc.) as attributes.

This way you can make user's claims available through you API. Now, for example, you can set $ctx.identity.cognitoIdentityId as the owner of an item. Then maybe other users can see the name of the owner via GraphQL resolvers.

If you need to access the user's claims in your resolver I'm afraid that doesn't seems to be possible at the moment. I have made a question about this as it would be very helpful for authorization: Group authorization in AppSync using IAM authentication

In this case, instead of using a resolver you could use Lambda as a data source and retrieve the user's claims from the above-mentioned User table.

It's all a bit difficult at the moment :)