WCF Interceptor Example

let me google that for you.
This will give you high level idea of interceptors: http://msdn.microsoft.com/en-us/library/dd744842(v=vs.110).aspx
and here is a example: http://msdn.microsoft.com/en-us/library/dd744837(v=vs.110).aspx

next time please try googling before posting a question :)