docs: def get_jwt(self, request):
          """Extract the JWT token from the authorisation header of the request.
  
          Returns the JWT token or None, if the token cannot be extracted.
  
          :param request: request object.
          :type request: :class:`morepath.Request`
          """
          try:
              authorization = request.authorization
          except ValueError:
              return None
          if authorization is None:
              return None
          authtype, token = authorization
          if authtype.lower() != self.auth_header_prefix.lower():
              return None
          return token