code: def _unpack_header(self, headers):
          
          jwt_header = headers.get(self.header_name)
          MissingTokenHeader.require_condition(
              jwt_header is not None,
              "JWT token not found in headers under '{}'",
              self.header_name,
          )
  
          match = re.match(self.header_type + r'\s*([\w\.-]+)', jwt_header)
          InvalidTokenHeader.require_condition(
              match is not None,
              "JWT header structure is invalid",
          )
          token = match.group(1)
          return token
docs: Unpacks a jwt token from a request header