This handles the scenario where the issuer of the token will not match the pool url if a custom endpoint_url is used
Also fixed an issue where the USERNAME may not be provided as part of the ChallengeParameters response as it is optional according to the Cognito docs.
LocalStack Cognito authoriser does not provide the USERNAME as part of the ChallengeParameters
This handles the scenario where the issuer of the token will not match the pool url if a custom endpoint_url is used
Also fixed an issue where the USERNAME may not be provided as part of the ChallengeParameters response as it is optional according to the Cognito docs. LocalStack Cognito authoriser does not provide the USERNAME as part of the ChallengeParameters