I have a B2C Custom Policy configured. This policy gives id token in the output response. There are four custom attributes defined in the custom policy. These custom attributes are not stored in B2C extensions app. The Id Token from B2C Custom Policy correctly gives these four custom attributes along-with standard Output Claims. Response type used in custom policy is ‘id_token’.
Now, I want to make use of this B2C Custom Policy in AWS Cognito User Pool. In a new user pool, I have added a Federated Identity Provider and configured with clientid, secret, issuer url, etc. settings. Issuer URL is in the format – https://{tenant-name}.b2clogin.com/{tenant-id}/b2c_1a_signup_signin/v2.0
In AWS Cognito app client setup, I have allowed ‘Implicit Grant’.
When I use Hosted UI to test this setup, I am correctly redirected to the B2C login screen. Once user credentials are entered, I am expecting the Id-Token as the response. However, I end up getting an error like – “error_description=No+access+token+in+OAuth+IdP+response&error=invalid_request”.

Kindly share details or any additional inputs needed.