如何授权来自其他应用程序的有效用户的请求

I have two web applications, app-A and app-B (both will be hosted on different servers). Now for a particular event in app-A, I need to call an URL to app-B so that app-B can do some processing. Inside app-A, I am following login/logout for authorizing users. So at app-A, everything is secure.I have two web applications, app-A and app-B (b