title: How to add a SAML identity provider to a ASP.NET MVC 5 website to be used as external authentication for another webapp at my company
body: <p>I have a legacy monolith ASP.NET MVC 5 application on .NET framework 4.7 and our team is building a new more modern application for areas of our webapp and it uses identityserver4 to complete openid/oauth authentication for users.</p>
  <p>For a variety of reasons its not currently practical to share a single IDP and change the legacy app to provision users to a central shared location.</p>
  <p>Is there some way that I can keep the forms authentication powering our legacy web app in place and add an SSO identity provider (I think thats the right term) so that it can be configured to act as an external authentication provider in IdentityServer much the same as how Facebook and Twitter can be registered?</p>
  <p>I've been looking at the various SSO packages and getting confused with terminology and what actually fits where.  I am considering going with the least invasive option to start and users would still authenticate to the legacy system but would allow for the new apps IDP to trigger authentication to the legacy apps identity provider for certain users as an option.</p>
  <p>Is something like this possible ?</p>