Dev build: 

IdentityServer is a framework and a hostable component that allows implementing single sign-on and access control for modern web applications and APIs using protocols like OpenID Connect and OAuth2. It supports a wide range of clients like mobile, web, SPAs and desktop applications and is extensible to allow integration in new and existing architectures.

Watch this for the big picture: Introduction to OpenID Connect, OAuth2 and IdentityServer.

Go to the documenation site.

OpenID Connect specification / OAuth2 specification

IdentityServer is designed as an OWIN/Katana component. By referencing the library or nuget you get a UseIdentityServer extension method for IAppBuilder that allows setting up IdentityServer in your OWIN host:

public void Configuration(IAppBuilder app)
{
    var options = new IdentityServerOptions
    {
        SigningCertificate = Certificate.Get(),
        Factory = Factory.Create()
    };

    app.UseIdentityServer(options);
}

For more information, e.g.

• support for MembershipReboot and ASP.NET Identity based user stores
• support for additional Katana authentication middleware (e.g. Google, Twitter, Facebook etc)
• support for EntityFramework based persistence of configuration
• support for WS-Federation
• extensibility

check out the documentation and the samples.

• Access Token Validation
• EntityFramework support
• MembershipReboot support
• ASP.Net Identity support
• WS-Federation plugin
• Samples

IdentityServer is built using the following great open source projects:

• ASP.NET Web API
• Autofac
• Json.Net
• LibLog
• Katana
• Web Protection Library
• XUnit
• License Header Manager

..and is supported by the following open source friendly companies:

• JetBrains
• Gitter
• Huboard
• AppVeyor
• MyGet

...and last but not least thanks to all contributors!