public Optional<String> getCredentials() {
        return Optional.ofNullable(credentials);
    }
Gets the Credentials required for invoking the authorizer, if any, in
the form of an ARN of an IAM execution role.

<p>For example, "arn:aws:iam::account-id:IAM_role".

@return Returns the optional credential ARN.
smithy-aws-apigateway-traits/src/main/java/software/amazon/smithy/aws/apigateway/traits/AuthorizerDefinition.java