User-742633084 posted
In addition to what Illeris mentioned, here is another web reference talking about using forms authentication with WCF REST service:
#REST, WCF 4, Forms Authentication, and Custom Clients (Part 1 of 3)
http://www.centrolutions.com/blog/post/2011/12/29/REST-WCF-4-Forms-Authentication-and-Custom-Clients-(Part-1-of-3).aspx
Also, the key point is that you need to have the WCF service enable ASP.NET compatiblity mode so that it can access those ASP.NET specific context data and object models. Here are some references explaining ASP.NET compatiblity mode and how it can helps
for WCF HTTP/REST based service:
#WCF Services and ASP.NET
http://msdn.microsoft.com/en-us/library/aa702682.aspx
#ASP.NET Compatibility Mode
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ttp://blogs.msdn.com/b/wenlong/archive/2006/01/23/516041.aspx