how to authenticate user with rest service-wcf WebHttpBindig?

I have a server-client project written in c#. I want to change the client side to a web client so we can open it with the browser. So I decided to make a WCF rest service that will replace the server side. The binding that I am using for the service is webHttpBinding. My problem is with the behavior of the service. The service data (vars etc..) is initialize after every call. If i add the [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)] it doesn't change anything. If I use [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)], it works but I guess that the service instance will be the same for every client.

I have a simple html web page that get a username and password from the client and post it to the service. The service check the Login info with the user database and response. My problem is that i can't save the user status as logged in or not because after every post/get method the service is reset.

what should I do?