Substitute IdentityServer3 login system

Question

Following @leastprivilege answer in my previous question, I concluded that neither are possible solutions:

• The login service doesn\'t support REST authentication

Answer 1

Solved it after some research. You'll need this three steps:

• A Owin Authentication middleware that redirects to the page you want, providing the protected state (this will let you finish the authentication process later). You can follow [Anders Abel tutorial]
• Custom user service that overrides the PreAuthentication method and sets the SignInMessage message.Idp with your middleware id. Code sample: check it here
• After the successful authentication, your page should redirect to the middleware callback with the state parameter. With the mentioned dummy middleware, it's set as /signing-dummy