Adding Support for External Authentication

Next we will add support for external authentication. This is really easy, because all you really need is an ASP.NET Core compatible authentication middleware.

ASP.NET Core itself ships with support for Google, Facebook, Twitter, Microsoft Account and OpenID Connect. In Addition you can find providers for many other authentication provider here.

Adding Google support

To be able to use Google for authentication, you first need to register with them. This is done at their developer console. Create a new project, enable the Google+ API and configure the callback address of your local IdentityServer by adding the /signin-google path to your base-address (e.g. http://localhost:5000/signin-google).

If you are running on port 5000 - you can simply use the client id/secret from the code snippet below, since this is pre-registered by us.

Start by adding the Google authentication middleware nuget to your project (Microsoft.AspNetCore.Authentication.Google).

Next we need to add the middleware to the pipeline. Order is important, the additional authentication middleware must run after IdentityServer but before MVC.

By default, we wire up a cookie middleware behind the scenes, so that the external authentication can store its outcome. You simply need to add the external authentication middleware to the pipeline and make it use the IdentityServerConstants.ExternalCookieAuthenticationScheme sign-in scheme:

app.UseGoogleAuthentication(new GoogleOptions
    AuthenticationScheme = "Google",
    DisplayName = "Google",
    SignInScheme = IdentityServerConstants.ExternalCookieAuthenticationScheme,

    ClientId = "",
    ClientSecret = "3gcoTrEDPPJ0ukn_aYYT6PWo"


When using external authentication with ASP.NET Core Identity, the SignInScheme must be set to "Identity.External" instead of IdentityServerConstants.ExternalCookieAuthenticationScheme.

Now run the MVC client and try to authenticate - you will see a Google button on the login page:


After authentication, you can see that the claims are now being sourced from Google data.


Further experiments

You can add an additional external provider. We have a cloud-hosted demo version of IdentityServer4 which you can integrate using OpenID Connect.

First add the Microsoft.AspNetCore.Authentication.OpenIdConnect NuGet package to your project.


Next add the middleware:

// middleware for external openid connect authentication
app.UseOpenIdConnectAuthentication(new OpenIdConnectOptions
    SignInScheme = IdentityServerConstants.ExternalCookieAuthenticationScheme,
    SignOutScheme = IdentityServerConstants.SignoutScheme,

    DisplayName = "OpenID Connect",
    Authority = "",
    ClientId = "implicit",

    TokenValidationParameters = new TokenValidationParameters
        NameClaimType = "name",
        RoleClaimType = "role"


The quickstart UI auto-provisions external users. IOW - if an external user logs in for the first time, a new local user is created, all the external claims are copied over and associated with the new user. The way you deal with such a situation is completely up to you though. Maybe you want to show some sort of registration UI first. The source code for the default quickstart can be found here.