title: django 2 custom jwt_get_username_from_payload_handler
body: <p>To validate the jwt token of auth0 in django, I use the following code in settings.py</p>
  
  <pre><code>def jwt_get_username_from_payload_handler(payload):
  
      return 'authuser'
  
  JWT_AUTH = {
      'JWT_PAYLOAD_GET_USERNAME_HANDLER': jwt_get_username_from_payload_handler,
      'JWT_PUBLIC_KEY': PUBLIC_KEY,
      'JWT_ALGORITHM': 'RS256',
      'JWT_AUDIENCE': API_IDENTIFIER,
      'JWT_ISSUER': JWT_ISSUER,
      'JWT_AUTH_HEADER_PREFIX': 'Bearer',
  }
  </code></pre>
  
  <p>where authuser is the username. So Instead of writing it directly I want to receive it in request header and pass it. Please help me in customising this function - jwt_get_username_from_payload_handler in such a way. TIA</p>