Hi,
If we use Form Authentication in Web Services, it needs to redirect user to a Login page to input the credit information.
To avoid it, we can use Window Authentication, which doesn't need user to input the credit information in the page, instead, we can use NetworkCredential object to pass those credentials in program.
We also use custom authentication, such as SoapHeader.
For more information, see http://www.15seconds.com/issue/020312.htm
I look forward to hearing from you.