Question: I'm looking into using Identity Server 4 for authentication within a C# based MVC application. I'd like to use accounts stored in Azure AD as a source of valid users but the documentation only seems to refer to Google and OpenID & only mentions Azure in passing.

Does anybody know of any good documentation and/or tutorials on how to use Azure AD in the context of using it with Identity Server 4?

Answer: 
You can use signin to Azure AD from IdentityServer just as you would use signin to IdentityServer from e.g. a Javascript or MVC app. 

I have done this recently, and all you need to do is register OpenIdConnect options to Azure Ad like this: 

```
public void ConfigureAuth(IAppBuilder app)
{
    app.SetDefaultSignInAsAuthenticationType(CookieAuthenticationDefaults.AuthenticationType);

    app.UseCookieAuthentication(new CookieAuthenticationOptions());

    app.UseOpenIdConnectAuthentication(
        new OpenIdConnectAuthenticationOptions
        {
            ClientId = clientId,
            Authority = authority,
            PostLogoutRedirectUri = postLogoutRedirectUri,
        });
}

```

More info about this here: <https://learn.microsoft.com/en-us/azure/active-directory/develop/active-directory-devquickstarts-webapp-dotnet>

You should then in your Login action call the ChallengeAsync method: 

```
var authenticationProperties = new AuthenticationProperties { RedirectUri = "your redirect uri" };
await HttpContext.Authentication.ChallengeAsync(your policy, authenticationProperties);

```

Then provide a callback method as a GET method then follow the External Login samples provided in IdentityServer samples: <https://github.com/IdentityServer/IdentityServer4.Samples/blob/dev/Quickstarts/4_ImplicitFlowAuthenticationWithExternal/src/QuickstartIdentityServer/Quickstart/Account/AccountController.cs>
IdentityServer4 has documentation with "Sign-in with External Identity Providers"

<http://docs.identityserver.io/en/latest/topics/signin_external_providers.html#state-url-length-and-isecuredataformat>

Unfortunately it is not complete but this is what I did:

`Startup.cs` for .NET 5, `Program.cs` for .NET 6:

```
services.AddAuthentication()
      .AddOpenIdConnect("aad", "Azure AD", options =>
            {
                options.ClientSecret = "<ClientSecret>";
                options.ResponseType = OpenIdConnectResponseType.Code;
                options.ClientId ="<ClientId>";
                options.Authority = "https://login.microsoftonline.com/<TenantId>/";
                options.CallbackPath = "/signin-oidc";
            })
        .AddIdentityServerJwt();

```

You will then see an external login under "Use another service to log in.":

[![enter image description here](https://i.stack.imgur.com/HG9I4.png)](https://i.stack.imgur.com/HG9I4.png)

When completing login you should see this message.

[![enter image description here](https://i.stack.imgur.com/oLcGC.png)](https://i.stack.imgur.com/oLcGC.png)

Default settings got stuck after clicking on `Register`. It was due to the new email not being confirmed. This could be solved with setting `SignIn.RequireConfirmedAccount = false`

```
services.AddDefaultIdentity<ApplicationUser>(options => 
    options.SignIn.RequireConfirmedAccount = true)

```

You could also use "Resend email confirmation" or set `EmailConfirmed` to true in `[dbo].[AspNetUsers]` for the new user.

Azure AD settings. You will also need to add a client secret under `Certificates & secrets`.

[![enter image description here](https://i.stack.imgur.com/qMSXX.png)](https://i.stack.imgur.com/qMSXX.png)

[![enter image description here](https://i.stack.imgur.com/ZESnc.png)](https://i.stack.imgur.com/ZESnc.png)