docs: def auth_scheme(self):
          """ If an Authorization header is present get the scheme
  
          It is expected to be the first string in a space separated
          list & will always be returned lowercase.
  
          :return: str or None
          """
  
          try:
              auth = getattr(self, 'auth')
              return naked(auth.split(' ')[0]).lower()
          except (AttributeError, IndexError):
              return None