One Login amongst multiple ASP.NET MVC applications Questions
<p>I have been working on an ASP.NET MVC 4 application that uses forms based authentication.  Users are validated against a membership provider based on a provider selection on the login form.  For example, at this moment there are two providers:  active directory and a custom provider that calls an external web service.  If the user is valid then we update information in our local users table, like last logon date, etc. If the user is valid and doesn’t exist in the local users table, we add them.  Once all of this is done we set a cookie and move on to the main content.  All of the controllers check <strong>User.Identity.IsAuthenticated</strong> and return to the login page if the test fails. </p>

<p>Now I am told that this application is going from a single web application to a multiple application solution.  Each application should exist independently from the others, share the same look and feel, and use the same login functionality.  Each application can require a new membership provider to be added.  We will also add data for limiting access to the applications.  One user may only have access to one of the applications while another user has access to all of them.</p>

<p>Setting up the data storage is not a problem.  Sharing the layout from one application to be used in the others is not a problem either.  What I am having trouble with is deciding how to “refactor” the login functionality such that adding a new membership provider and application “down the road” will not require us to republish existing applications.  Right now they would also not want a single sign-on launch page for the applications.  They would like for the users to go straight to an application, login, and do what they came there to do.  Thus, I may go to <a href="http://site1.mysites.com" rel="nofollow">http://site1.mysites.com</a>, login and do my work while the guy next to me goes to <a href="http://site2.mysites.com" rel="nofollow">http://site2.mysites.com</a>, logs in and does his work.  </p>

<p>I am having trouble wrapping my head around the best way to do this.  My first thought was a WCF web service for the login.  I would have a controller action call the webservice passing the login credentials.  If the login was successful, then I could get a list of applications for the user from the local storage.  Adding more applications would not require us to republish existing apps due to no changes in the web service for those apps.  </p>

<p>I also keep hearing about this ASP.NET Web API stuff.  Should I go that route instead?  I may want to build a site around administering the local user database so having a site that hosted the web api could be an option.  </p>

<p>Is the Web API stuff wrong for this situation?  If not, does it hold advantages over the WCF web service?  Are there alternative methods of achieving my end result?</p>
