How do I share session state built by ASP.NET application with php on the same IIS?

Answer 1

You don't. Even if you could share simple stuff (which you probably can do if you write your own file-based or database-driven session management system), you still cannot pass serialized arrays or objects between the two.

Alternatively, you could look into extending ASP.Net to include PHP:

http://www.php-compiler.net/

This way, you can write .Net assemblies (and import .Net classes) in PHP...