title: How to throw custom error message from API Gateway custom authorizer
body: <p><a href="https://github.com/awslabs/aws-apigateway-lambda-authorizer-blueprints/blob/master/blueprints/python/api-gateway-authorizer-python.py#L30-L31" rel="noreferrer">Here</a> in the blue print says, API gateway will respond with 401: Unauthorized. </p>
  
  <p>I wrote the same <code>raise Exception('Unauthorized')</code> in my lambda and was able to test it from Lambda Console. But in POSTMAN, I'm receiving status <code>500</code> 
  with body: </p>
  
  <pre><code>{
    message: null`
  } 
  </code></pre>
  
  <p>I want to add custom error messages such as "Invalid signature", "TokenExpired", etc., Any documentation or guidance would be appreciated.</p>