Cuurently I am using "wcservice" authenticator for my webscript and in this case it displays me the default login page and after giving the user credential it executes the webscript.
I want to pass the username and password with the webscript URL and it should validate and execute the webscript.
You don't need a custom authenticator for that. If you use "/service" instead of "/wcservice" you can pass the username and password in the HTTP headers using HTTP Basic authentication.
Additionally, if you're not using MSIE you can also add the username and password at the start of the URL*. MSIE disables this by default, but it can be enabled either on a PC-by-PC basis, or using group policy.