ASP.NET Web API and OpenID Connect: how to get Access Token from Authorization Code

Question

I try to get OpenID Connect running... A user of my Web API managed to get an Authorization Code of a OpenID Connect Provider. How am I supposed to pass this code to my ASP.NET Web API? How do I have to configure OWIN Middleware such that I can get an Access Token using the Authorization Code?

UPDATE: A SPA uses AJAX for communicating with my web service (ASP.NET Web API). In my web service a use OWIN Middleware. I set OpenIDConnect as the authentication mechanism. When the web service is called for the first time it successfully redirected the user to the login page of the OpenID Connect Provider. The user could login and got an Authorization Code as a result. AFAIK this code could now be used (by my web service) to the an Access Token. However, I don't know how to get this code back to my web service (is this done using a header?) and then what to configure to get the Access Token. I guess I could call the token endpoint manually but I would like to take advantage of the OWIN component instead.

Answer 1

BenV already answered the question, but there's more to consider.

class partial Startup
{
    public void ConfigureAuth(IAppBuilder app)
    {
        // ...

        app.UseOpenIdConnectAuthentication(new OpenIdConnectAuthenticationOptions
          {
            ClientId = clientId,
            Authority = authority,
            Notifications = new OpenIdConnectAuthenticationNotifications() {
                AuthorizationCodeReceived = (context) => {
                   string authorizationCode = context.Code;
                   // (tricky) the authorizationCode is available here to use, but...
                   return Task.FromResult(0);
                }
            }
          }
    }
}

Two problems:

• First of all, authorizationCode will get expired quickly. There's no sense in storing it.
• The second problem is that AuthorizationCodeReceived event will not get fired for any of the page reloads as long as authorizationCode is not expired and stored inside the session.

What you need to do is to call AcquireTokenByAuthorizationCodeAsync which will cache it and handle properly inside TokenCache.DefaultShare:

AuthorizationCodeReceived = (context) => {
    string authorizationCode = context.Code;
    AuthenticationResult tokenResult = await context.AcquireTokenByAuthorizationCodeAsync(authorizationCode, new Uri(redirectUri), credential);
    return Task.FromResult(0);
}

Now, before every call to the resource, invoke AcquireTokenSilentAsync to get the accessToken (it will use TokenCache or silently use refreshToken ). If token is expired, it will raise AdalSilentTokenAcquisitionException exception (invoke access code renew procedure).

// currentUser for ClaimsPrincipal.Current.FindFirst("http://schemas.microsoft.com/identity/claims/objectidentifier")
AuthenticationResult authResult = await context.AcquireTokenSilentAsync(resourceUri, credential, currentUser);

Calling AcquireTokenSilentAsync is very fast if token is cached.

Answer 2

Looks like the recommended approach is to use the AuthorizationCodeReceived event to exchange the Auth code for an Access Token. Vittorio has a blog entry that outlines the overall flow.

Here's an example from this sample app on GitHub of the Startup.Auth.cs code to set this up:

app.UseOpenIdConnectAuthentication(
    new OpenIdConnectAuthenticationOptions
    {
        ClientId = clientId,
        Authority = Authority,
        Notifications = new OpenIdConnectAuthenticationNotifications()
        {
            AuthorizationCodeReceived = (context) =>
           {
               var code = context.Code;
               ClientCredential credential = new ClientCredential(clientId, appKey);
               string tenantID = context.AuthenticationTicket.Identity.FindFirst("http://schemas.microsoft.com/identity/claims/tenantid").Value;
               string signedInUserID = context.AuthenticationTicket.Identity.FindFirst(ClaimTypes.NameIdentifier).Value;
               AuthenticationContext authContext = new AuthenticationContext(string.Format("https://login.windows.net/{0}", tenantID), new EFADALTokenCache(signedInUserID));
               AuthenticationResult result = authContext.AcquireTokenByAuthorizationCode(
                           code, new Uri(HttpContext.Current.Request.Url.GetLeftPart(UriPartial.Path)), credential, graphResourceID);

               return Task.FromResult(0);
            },
            ...
    }

Note: The AuthorizationCodeReceived event is invoked only once when authorization really takes place. If the auth code is already generated and stored, this event is not invoked. You have to logout or clear cookies to force this event to take place.

Answer 3

You need to bypass the default owin validation to do custom Authorization:

           new OpenIdConnectAuthenticationOptions
            {
                ...,
                TokenValidationParameters = new System.IdentityModel.Tokens.TokenValidationParameters
                {
                    ValidateIssuer = false
                },