Silverlight Session Management, Error handling, and Unit Test of WCF service

AcknowledgementI had the following requirements:Session management.In the second web service call, i want to know something from the first callImpersonate userI don't want to enter my credentials if my service has to work as my user. Error handlingit’s not very cool to get a white website after an error occurs.Unit tests of the wcf serviceIt would be great to have tests for the stuff aboveLet's