OAuth2 in Thinktecture IdentityServer v2: Using the Implicit Flow with Windows Store Clients

WinRT has built-in support for the “browser control/redirect” sign-in mechanism that is used in OAuth2 implicit flow. The API for that is called the WebAuthenticationBroker and using it has some advantages, e.g.

  • Give the user a consistent interface for entering credentials (though I don’t know how hard it would be to spoof such an interface).
  • The app itself never sees the password, just the token that gets returned by the handshake.
  • The container that does the web interaction has separate cookie management and integrates with the Windows 8 capabilities sandbox. This includes capabilities like network access restrictions and sending Windows credentials.

Setting up a resource/client for WebAuthenticationBroker works exactly the same as for a JavaScript client – see Christian’s post.

In your Windows Store app, you then construct a request URL, e.g.:

var startUri = new Uri(
 
string
.Format(
   
“{0}?client_id={1}&scope={2}&redirect_uri={3}&response_type=token”
,

      endpoint.AbsoluteUri,

      Uri.EscapeDataString(clientId),

      Uri.EscapeDataString(scope),

      Uri.EscapeDataString(callbackUri.AbsoluteUri)));

 

You also have to tell the broker how to detect when the handshake is done. There are multiple ways to do this, either wait for a specific redirect URI, wait for a POST or looking for something in the title bar. The most common option would be the redirect URI.

If you don’t specify a specific redirect URI, the broker is looking for the app specific App-Id (in the ms-app:// format). You can query that value by calling WebAuthenticationBroker.GetCurrentApplicationCallbackUri().

You don’t have to use the ms-app:// ID, but this allow the broker container to maintain a cookie with the token service, which might be useful.

So in the end, you can invoke the broker e.g. like this:

var result = await WebAuthenticationBroker.AuthenticateAsync(

        WebAuthenticationOptions.None,

        startUri);

This will render the sign-in and consent UI:

broker consent

After that, the result variable will contain the redirect URI including the query string/hash fragment – and you can then retrieve the access token or authorization code from there.

In addition you can combine that with WinRT’s PasswordVault to securely store the access token – and maybe even sync it across multiple devices.

You can find the complete sample here.

HTH

This entry was posted in IdentityModel, IdentityServer, OAuth, WebAPI. Bookmark the permalink.

6 Responses to OAuth2 in Thinktecture IdentityServer v2: Using the Implicit Flow with Windows Store Clients

  1. This is awesome! I am curious though, using the Identity Server’s OAuth2 endpoint (https://idsrv.myapp.com/issue/oauth2/authorize), when the user is prompted for the login screen, is he able to use different identity providers? I’ve set identity providers up, however, I don’t see any options besides username and password.

  2. Mark Biagio says:

    I have an issue where Win8 says “cannot locate the resource” and does not show the Idsrv login screen. Ive checked the setup, rerplaced your sample project with my settings and the same thing. If i copy and paste the oauth2 authorize endpoint url with parameters (client_id etc) from my java code into my browser, i get the login screen, asking for permission etc. What am i doing wrong? Thanks.

    • For reasons unknown to me – Win8 does not support to have the STS on the local machine. You need to run it on a different server.

      • Mark Biagio says:

        Thanks, deployed idsrv to azure with ssl etc etc and its working

      • Alan Pulliam says:

        Going to give this a try. I’ve been pulling out my hair trying to figure out why WeAuthenticationBroker won’t hit my local Authorization Server.

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