ESO Authentication on IIS for PHP and .NET applications (Shibboleth / SAML / WiF ...)
I don't know much about single sign in but check The DOTNET class
The DOTNET class allows you to instantiate a class from a .Net assembly and call its methods and access its properties.
$obj = new DOTNET("assembly", "classname")
So you can keep authentication @ single library of DOT NET to support both PHP and ASPX with one authentication method.
<?php $stack = new DOTNET("mscorlib", "System.Collections.Stack"); $stack->Push(".Net"); $stack->Push("Hello "); echo $stack->Pop() . $stack->Pop();?>