I have a c# application that defines a membership provider used in a Asp.Net MVC application.
And i have an apache httpd server that does authentication with mod_wsgi.
The objective is to share the membership provider between the two, so that the authentication information be the same.
How can i achieve this behaviour ?
Trivially.

Apache serves static content.
Certain URI's will be routed to mod_wsgi to Python.
Python will then execute (via subprocess) a C# program, providing command-line arguments, and reading the standard output response from the C# program.
Python does whatever else is required to serve the web pages.

This presumes your C# application runs at the command line, reads command-line parameters and writes its result to standard output.  This is an easy thing to build.  It may not be the way it works today, but any program that runs from the command line is trivial to integrate.
Your C# application, BTW, can also be rewritten into Python.  It isn't magic.  It's just code.  Read the code, understand the code, and translate the code.  You'll be a lot happier replacing the C# with something simpler.
using c# inside an apache python script