The following custom solution is built using ASP.NET to provide an authentication mechanism using SOAP headers. The solution involves a custom Extending ASP.NET Processing with HTTP Modules on the Web server that executes the following steps:
The HTTP Module parses HTTP messages to check whether they are SOAP messages.
If the HTTP Module detects a SOAP message, it reads the SOAP headers.
If the SOAP message has the SOAP header with authentication credentials, HTTP Module raises a custom global.asax event.

ref
http://msdn2.microsoft.com/en-us/library/9z52by6a.aspx