API Gateway does not have permissions to invoke Custom Authorizer by default

I have created a custom authorizer in my application (actually declared in a BluePrint).
`CustomAuthorizer(
'DocManCustomAuth', header='Authorization',
authorizer_uri=(auth_arn))`
However, when I package and deploy the function (using cloudformation), all authorizations fail with:
`Execution failed due to configuration error: Invalid permissions on Lambda function
Fri Mar 20 06:28:55 UTC 2020 : Execution failed due to configuration error: Authorizer error
Fri Mar 20 06:28:55 UTC 2020 : AuthorizerConfigurationException
`
I have to delete all references and add another authorizer (pointing to the same function) manually to work. When adding the authorizer, I am given the choice on API Gateway console to give the requisite permissions to API Gateway to invoke the lambda function. That's when it starts working.

Start by tracing how the BluePrint CustomAuthorizer and CloudFormation deployment define the authorizer and its Lambda permissions. Compare that generated configuration with the permission added through the API Gateway console; done means a newly deployed custom authorizer accepts requests without manually deleting and recreating it.

Written by the indexing model from the issue text.