Problem with Custom Authorizers

I'm trying to implement a custom authorizer and so far, it has gone very well and it's all working perfectly fine.

However, the one major issue I am having is that I cannot return a custom error message if the authenticator fails. I am having the return the following for every error at the moment:

`return &events.APIGatewayCustomAuthorizerResponse{}, errors.New("Unauthorized")`.

If I try any other error message, I get `{"message": null}` as the response on my client. Is there any way to customize this error message (preferably without using the AWS console as I'd like it to be automated)?