expose only some methods of webservice

Either you need to develop different service for different client. But the disadvantage is it will difficult to manage when more client will come into picture.

 

Follow below link that will help you implement authenatication in WCF service:

 

https://randypaulo.wordpress.com/2011/07/13/wcf-using-windows-authentication-and-sqlroleprovider-over-basichttp/

 

Secondly, you need to imlement authorization when you get any request from client. Check the method in the request header and also ask client to send their user name with header. So that you will check the method with respective user. Please follow below links that may help you:

 

http://stackoverflow.com/questions/10248482/how-to-log-the-raw-request-in-wcf-service

 

http://stackoverflow.com/questions/18877591/how-to-read-http-request-headers-in-a-wcf-web-service