How to share sessions between PHP and ASP.net application?

My company took some old php application over. Due to our preference to ASP.net and to the lack of any documentation from the previous developer, we do not want to spend much resources on developing in PHP.
For implementing new features, we will create an Asp.net application that has the same look to the user. We want to develop a kind of ‘coexisting’ web application. Therefore we must share sessions between an PHP and an Asp.net webapplication project, because there is a usermanagement involved with an existing MySQL database.

ASP.NET to WordPress SSO with HttpWebRequest

I am attempting to create a single sign on experience between an asp.net site and a wordpress site using a simple form POST method. I have built a simple php page that uses the native wordpress functions wp_insert_user and wp_signon to create user account in the mysql db and sign them in. In my asp.net ‘create new user’ page code behind, I’m using the post method of an HttpWebRequest to send the required information to the php page.