AWS API Gateway Custom Authorizer AuthorizerConfigurationException

AuthorizerConfigurationException is usually an indication that API Gateway failed to call your authorizer due a permissions error.

Please either make sure you've properly configured your function to be invoked by API Gateway. An easy to reset this is by removing and re-adding the function to your authorizer. The console will then prompt you to add the necessary permissions.

Figured out what was causing the issue. From python lambda function, I was returning a json string instance. Instead it should be json object. Its strange that the same lambda function did not error when I tested the API from API Gateway "test" feature. But when the API was called from internet (curl or chrome) it failed.

#return policy_string ... this is incorrect.
return json.loads(policy_string)