WSO2 APIM feedback error code and message

Using WSO2 api manager (1.7.0), how do I send an error message with a basic message to the client?

An example . When the backend api service responds with a 401 error, the API gateway sends another "500 Internal Server Error" message to the client.

Is there a way WSO2 APIM sends the actual "401 - Unauthorized" message to the client.

Details:

• The client sends a POST request to WSIM2 APIM with the authorization and authentication headers.

• WSO2 APIM removes the authorization header and converts the authentication header into an authorization header before sending the request to the backend server.

• The backend server responds with a "401 - Unauthorized" error message on WSO2 APIM

• WSO2 APIM responds to the client with another message - "500 Internal server error".