Here are the steps the client, Web Interface and Citrix service all combine to give you a session:
- The user logs on the Web Interface (WI)
- Web interface speaks to the XML broker, and passes the credentials
- The XML broker reaches out to an Active Directory Domain Controller with the credentials to authenticate
- If you pass authentication the WI will enumerate the applications and desktops you have. At this point a user can start/select an application to run
- A server will respond back to the WI with ICA file for the app/desktop
- The ICA file is passed from WI to the client machine
- Client machine open the ICA and reaches out directly to the given XenApp/XenDesktop device
- The XenApp Server confirms the correct RDS/TS License is available
- The standard Windows computer logon starts (RDS or XD session)
- XenApp/DDC checks with the Citrix license server to obtain a licence
- The Microsoft GPO’s are applied
- The Citrix policies are applied
- The remaining standard Windows logon process run, FirstRun, Run, Startup etc
- The user is happy…
Much of this detail came from here and here: