I\'m developing an MVC 4 web application in C# and want to handle login using an existing SAML 2.0 identity provider. I am using HTTP POST binding with SimpleSAMLphp.
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You're right in that WIF (now moved into core .NET under System.IdentityModel) only supports the SAML2 tokens and not the SAML2 protocols required to implement a service provider.
Kentor.AuthServices is an open source SP implementation for ASP.NET MVC built on top of .NET 4.5. Install the package and add some settings in web.config - no coding required.
Disclaimer: I'm the author of Kentor.AuthServices