How to provide authentication to a webservice

Hi Team,

I have created couple of webservices using powerbuilder 12.5(.Net) .Now i want to secure this WSDLs by providing some userid and password means if i browse this WSDLs in the internet explore,it should ask for Userid and password, and after that the XML page should be open.

Can anybody please help me on this how to acheieve this one ?

Thanks in Advance.

Regards

Subrat