Configure the authorization server endpoint

EDIT (01/28/2021): AspNet.Security.OpenIdConnect.Server has been merged into OpenIddict as part of the 3.0 update. To get started with OpenIddict, visit documentation.openiddict.com.

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Okay, let’s recap the different OAuth2 middleware (and their respective IAppBuilder extensions) that were offered by OWIN/Katana 3 and the ones that will be ported to ASP.NET Core:

• app.UseOAuthBearerAuthentication/OAuthBearerAuthenticationMiddleware: its name was not terribly obvious, but it was (and still is, as it has been ported to ASP.NET Core) responsible for validating access tokens issued by the OAuth2 server middleware. It’s basically the token counterpart of the cookies middleware and is used to protect your APIs. In ASP.NET Core, it has been enriched with optional OpenID Connect features (it is now able to automatically retrieve the signing certificate from the OpenID Connect server that issued the tokens).

Note: starting with ASP.NET Core beta8, it is now namedapp.UseJwtBearerAuthentication/JwtBearerAuthenticationMiddleware.

• app.UseOAuthAuthorizationServer/OAuthAuthorizationServerMiddleware: as the name suggests, OAuthAuthorizationServerMiddleware was an OAuth2 authorization server middleware and was used to create and issue access tokens. This middleware won’t be ported to ASP.NET Core: OAuth Authorization Service in ASP.NET Core.

• app.UseOAuthBearerTokens: this extension didn’t really correspond to a middleware and was simply a wrapper around app.UseOAuthAuthorizationServer and app.UseOAuthBearerAuthentication. It was part of the ASP.NET Identity package and was just a convenient way to configure both the OAuth2 authorization server and the OAuth2 bearer middleware used to validate access tokens in a single call. It won’t be ported to ASP.NET Core.

ASP.NET Core will offer a whole new middleware (and I’m proud to say I designed it):

• app.UseOAuthAuthentication/OAuthAuthenticationMiddleware: this new middleware is a generic OAuth2 interactive client that behaves exactly like app.UseFacebookAuthentication or app.UseGoogleAuthentication but that supports virtually any standard OAuth2 provider, including yours. Google, Facebook and Microsoft providers have all been updated to inherit from this new base middleware.

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So, the middleware you’re actually looking for is the OAuth2 authorization server middleware, aka OAuthAuthorizationServerMiddleware.

Though it is considered as an essential component by a large part of the community, it won’t be ported to ASP.NET Core.

Luckily, there’s already a direct replacement: AspNet.Security.OpenIdConnect.Server (https://github.com/aspnet-contrib/AspNet.Security.OpenIdConnect.Server)

This middleware is an advanced fork of the OAuth2 authorization server middleware that comes with Katana 3 but that targets OpenID Connect (which is itself based on OAuth2). It uses the same low-level approach that offers a fine-grained control (via various notifications) and allows you to use your own framework (Nancy, ASP.NET Core MVC) to serve your authorization pages like you could with the OAuth2 server middleware. Configuring it is easy:

ASP.NET Core 1.x:

// Add a new middleware validating access tokens issued by the server.
app.UseOAuthValidation();

// Add a new middleware issuing tokens.
app.UseOpenIdConnectServer(options =>
{
    options.TokenEndpointPath = "/connect/token";

    // Create your own `OpenIdConnectServerProvider` and override
    // ValidateTokenRequest/HandleTokenRequest to support the resource
    // owner password flow exactly like you did with the OAuth2 middleware.
    options.Provider = new AuthorizationProvider();
});

ASP.NET Core 2.x:

// Add a new middleware validating access tokens issued by the server.
services.AddAuthentication()
    .AddOAuthValidation()

    // Add a new middleware issuing tokens.
    .AddOpenIdConnectServer(options =>
    {
        options.TokenEndpointPath = "/connect/token";

        // Create your own `OpenIdConnectServerProvider` and override
        // ValidateTokenRequest/HandleTokenRequest to support the resource
        // owner password flow exactly like you did with the OAuth2 middleware.
        options.Provider = new AuthorizationProvider();
    });

There’s an OWIN/Katana 3 version, and an ASP.NET Core version that supports both .NET Desktop and .NET Core.

Don’t hesitate to give the Postman sample a try to understand how it works. I’d recommend reading the associated blog post, that explains how you can implement the resource owner password flow.

Feel free to ping me if you still need help.
Good luck!