How to include userid, pass to WifiClient connect() api
WifiClient provides low level tcp connection. Your server seems to be implementing a REST API interface. Thus you need to construct HTTP headers (GET, POST, etc.) manually as a string. Then you can add your credentials. Before doing so, try to use your server, I mean call api's with the program named Postman. Postman runs on Chrome browser. Postman can compose such headers for you. Then you can insert them into your arduino code.