WCF: define which webservice can be accessed

Hello,

 I have created an application, with a layer that has multiple wcf(web services). Let's say WebService1, Webservice2, Webservice3, Webservice4, and Webservice5.

Webservice1, 2 and 3 can be called with same certificate. The issue is the caller to Webservice1, can also access Webservice2 and 3.

What I want is the caller to Webservice1, use only Webservice1 and be denied access to Webservice2 and 3, keeping same certificate.

What are the options?

Thanks in advance

Al