code: def create_token_response(self, request, token_handler):
          
          headers = self._get_default_headers()
          try:
              if self.request_validator.client_authentication_required(request):
                  log.debug('Authenticating client, %r.', request)
                  if not self.request_validator.authenticate_client(request):
                      log.debug('Client authentication failed, %r.', request)
                      raise errors.InvalidClientError(request=request)
              elif not self.request_validator.authenticate_client_id(request.client_id, request):
                  log.debug('Client authentication failed, %r.', request)
                  raise errors.InvalidClientError(request=request)
              log.debug('Validating access token request, %r.', request)
              self.validate_token_request(request)
          except errors.OAuth2Error as e:
              log.debug('Client error in token request, %s.', e)
              headers.update(e.headers)
              return headers, e.json, e.status_code
  
          token = token_handler.create_token(request, self.refresh_token)
  
          for modifier in self._token_modifiers:
              token = modifier(token)
  
          self.request_validator.save_token(token, request)
  
          log.debug('Issuing token %r to client id %r (%r) and username %s.',
                    token, request.client_id, request.client, request.username)
          return headers, json.dumps(token), 200
docs: Return token or error in json format.
  
          :param request: OAuthlib request.
          :type request: oauthlib.common.Request
          :param token_handler: A token handler instance, for example of type
                                oauthlib.oauth2.BearerToken.
  
          If the access token request is valid and authorized, the
          authorization server issues an access token and optional refresh
          token as described in `Section 5.1`_.  If the request failed client
          authentication or is invalid, the authorization server returns an
          error response as described in `Section 5.2`_.
  
          .. _`Section 5.1`: https://tools.ietf.org/html/rfc6749#section-5.1
          .. _`Section 5.2`: https://tools.ietf.org/html/rfc6749#section-5.2