I have a solution with an existing web forms website project (NOT web application project). I want to add a new mvc web application to the solution and have web forms site and mvc web app share forms authentication. I followed the article from microsoft but on localhost this does not work. In the solution, if I start both the webforms and mvc sites they have different port numbers for localhost so I authenticate in the webforms web site but the authentication cookie does not get picked up. Is there something obvious I am missing?