how to use session in silverlight application ?

Question

i am developing an software in silverlight 5 and facing some problem regarding session.
i am using child window and calling it from the page load. child window is for the login into the system that i am developing.  i need to hold the username who logged into the system through out the pages that i am going to create. can anyone please help me to or walk through with me on sessions in silverlight. Thanks!!