In Amazon Cognito, your mobile app authenticates with the Identity Provider (IdP) using the provider’s SDK. Once the end-user is authenticated with the IdP, the OAuth or OpenID Connect token returned from the IdP is passed by your app to Amazon Cognito. In addition to the access token, which of the following is returned for the user to provide a set of temporary, limited-privilege AWS credentials?

Answer options:

A.Cognito SDK
B.Cognito Key Pair
C.Cognito Identity ID
D.Cognito API

Answer - C
If you`re allowing unauthenticated users, you can retrieve a unique Amazon Cognito identifier (identity ID) for your end-user immediately. If you`re authenticating users, you can retrieve the identity ID after setting the login tokens in the credentials provider.
For more information on Cognito ID, please refer to the below link.
http://docs.aws.amazon.com/cognito/latest/developerguide/getting-credentials.html