code: public Response tokenIssue(String ticket, String subject, Property[] properties)
      {
          // Call Authlete's /api/auth/token/issue API.
          TokenIssueResponse response = callTokenIssue(ticket, subject, properties);
  
          // 'action' in the response denotes the next action which
          // this service implementation should take.
          TokenIssueResponse.Action action = response.getAction();
  
          // The content of the response to the client application.
          String content = response.getResponseContent();
  
          // Dispatch according to the action.
          switch (action)
          {
              case INTERNAL_SERVER_ERROR:
                  // 500 Internal Server Error
                  return ResponseUtil.internalServerError(content);
  
              case OK:
                  // 200 OK
                  return ResponseUtil.ok(content);
  
              default:
                  // This never happens.
                  throw unknownAction("/api/auth/token/issue", action);
          }
      }
docs: Issue an access token and optionally an ID token.
  This method calls Authlete's {@code /api/auth/token/issue} API.