AuthorizationCodeProvider: Create is never called, how do I generate the authorization code?

Question

I'm setting up my own OAuth2 server. So far, I have succesfully implemented GrantResourceOwnerCredentials in my implementation of OAuthAuthorizationServerProvider. Now, because I am developing an app for our business, I want to implement the OAuth2 Authorization Code grant.

I have tried to follow directions here https://docs.microsoft.com/en-us/aspnet/aspnet/overview/owin-and-katana/owin-oauth-20-authorization-server but in my implementation, I have not found how to reach the Create call of the AuthorizationCodeProvider (which I set in OAuthAuthorizationServerOptions).

I have briefly checked whether accessing the TokenEndpointPath with a (wrong) code parameter works, and in the debugger I see that my AuthorizationCodeProvider's Receive call is hit. Of course there is no success because the code I send is 'sometestcode' instead of a real one, but the code is hit so that means I'm on the right path.

Here's what I have so far:

    public override Task ValidateClientRedirectUri(OAuthValidateClientRedirectUriContext context)
    {
        if (OAuthRepository.GetClient(context.ClientId) != null)
        {
            var expectedRootUri = new Uri(context.Request.Uri, "/");

            if (context.RedirectUri.StartsWith(expectedRootUri.AbsoluteUri))
            {
                context.Validated();
                return Task.FromResult<object>(null);
            }
        }

        context.Rejected();
        return Task.FromResult<object>(null);
    }

    public override Task AuthorizeEndpoint(OAuthAuthorizeEndpointContext context)
    {
        // I know this is wrong but it's just a start and not the focus of this SO question.
        context.Response.Redirect(context.AuthorizeRequest.RedirectUri);
        context.RequestCompleted();
        return Task.FromResult<object>(null);
    }

    public override Task GrantAuthorizationCode(OAuthGrantAuthorizationCodeContext context)
    {
        // Needs additional checks, not the focus of my question either 
        var newTicket = new AuthenticationTicket(context.Ticket.Identity, context.Ticket.Properties);
        context.Validated(newTicket);
        return Task.FromResult<object>(null);
    }

Now, when I call my AuthorizeEndpointPath with a redirect_uri, I am sent to that Uri immediately. I know this is wrong: I should be sent to a separate login page. I'll fix my Web API later to redirect to the correct Uri.

The focus of my question is this: I am now in the process of implementing the login page, but I do not know how to get the authorization code from my WebAPI after the user has logged in. (I'm skipping the consent part for now and assume that if the user is logged in they're okay with it, I'll add giving consent later.)

I am basing my flow on the diagram shared here https://docs.apigee.com/api-platform/security/oauth/oauth-v2-policy-authorization-code-grant-type

I am using Thinktecture IdentityModel to create the login page in an MVC Controller. Now I need to retrieve the authorization code from the Web API in my MVC Controller. And after that I can then redirect the user back to the original client (app) that requested the Authorization Code flow.

To obtain the authorization code from my Web API, I see three methods in Thinktecture's OAuth2Client:

• CreateAuthorizeUrl
• CreateCodeFlowUrl
• RequestAuthorizationCodeAsync

Neither seem to do what I want. How do I proceed so that my WebAPI is called to generate the code?

    [HttpGet]
    [ImportModelStateFromTempData]
    public ActionResult Authorize(string clientId, string returnUrl, string responseType)
    {
        AuthorizeViewModel viewModel = new AuthorizeViewModel();
        ...
        ... 
        ...
        return View(viewModel);
    }

    [HttpPost]
    [ExportModelStateToTempData]
    public async Task<ActionResult> Authorize(AuthorizeViewModel viewModel)
    {
        // NOTE: This is in MVC and is postback from *.cshtml View.
        OAuth2Client.?????? // <=== How to obtain authorization code from WebAPI?

        ...
        return Redirect(returnUrl);
    }

I think I have it correctly setup on the Web API side. I just don't know how to hit the Create part of the flow. I hope someone can help me understand what I am not seeing. I have a blind spot somewhere I think...

How do I have OAuth2Client get me the authorization code from my WebAPI?

I am also using Postman to test my Web API. If anyone can help me get the URL in Web API 2.0 that returns an authorization code, I would also accept that as an answer. Then I can write the code in MVC myself.

Edit

Okay, so I think I found a part of my blind spot. Firstly, I marked `AuthorizeEndpoint' as "not the focus of this SO question", but that was a big mistake.

When I adapt the AuthorizeEndpoint like so:

    public override Task AuthorizeEndpoint(OAuthAuthorizeEndpointContext context)
    {
        System.Security.Claims.ClaimsIdentity ci = new System.Security.Claims.ClaimsIdentity("Bearer");
        context.OwinContext.Authentication.SignIn(ci);
        context.RequestCompleted();
        return Task.FromResult<object>(null);
    }

And if I adapt my implementation of AuthorizationCodeProvider.Create like so:

    public void Create(AuthenticationTokenCreateContext context)
    {
        context.Ticket.Properties.IssuedUtc = DateTime.UtcNow;
        context.Ticket.Properties.ExpiresUtc = DateTime.UtcNow.AddSeconds(60);

        // Some random Guid
        context.SetToken(Guid.NewGuid().ToString("n"));
    }

Any call to /authorize is redirected to redirect_uri with a query parameter code=<THE_RANDOM_GUID>! :D

Obviously, this implementation is not where it should be, so my question is not yet resolved. Remaining issues:

• Right now, anybody can request an authorization code, the client_id is ignored. ValidateClientAuthentication is apparently not hit as part of AuthorizeEndpoint. How do I obtain ClientId in AuthorizeEndpoint?
• The authorization code is not coupled to a client. Anyone who intercepts the code could use it. How do I obtain the ClientId in AuthorizationCodeProvider.Create so that I can store it with the code?
• The authorization code is not coupled to a user at all, it's an empty ClaimsIdentity. How do I put a user-login page in between and in AuthorizeEndpoint obtain the ClaimsIdentity for the logged-in user?

Answer 1

So, after quite some searching online, I got some success by searching github. Apparently, OAuthAuthorizationServerProvider offers AuthorizeEndpoint and that method should be used for both "Hey, you're not authorized, go log in you!" as well as for "Ahh, okay you're cool, here's an authorization code.". I had expected that OAuthAuthorizationServerProvider would have two separate methods for that, but it doesn't. That explains why on github, I find some projects that implement AuthorizeEndpoint in a rather peculiar way. I've adopted this. Here's an example:

public override async Task AuthorizeEndpoint(OAuthAuthorizeEndpointContext context)
{
    if (context.Request.User != null && context.Request.User.Identity.IsAuthenticated)
    {
        var redirectUri = context.Request.Query["redirect_uri"];
        var clientId = context.Request.Query["client_id"];

        var authorizeCodeContext = new AuthenticationTokenCreateContext(
            context.OwinContext, 
            context.Options.AuthorizationCodeFormat,
            new AuthenticationTicket(
                (ClaimsIdentity)context.Request.User.Identity,
                new AuthenticationProperties(new Dictionary<string, string>
                {
                    {"client_id", clientId},
                    {"redirect_uri", redirectUri}
                })
            {
                IssuedUtc = DateTimeOffset.UtcNow,
                ExpiresUtc = DateTimeOffset.UtcNow.Add(context.Options.AuthorizationCodeExpireTimeSpan)
            }));

        await context.Options.AuthorizationCodeProvider.CreateAsync(authorizeCodeContext);

        context.Response.Redirect(redirectUri + "?code=" + Uri.EscapeDataString(authorizeCodeContext.Token));
    }
    else
    {
        context.Response.Redirect("/account/login?returnUrl=" + Uri.EscapeDataString(context.Request.Uri.ToString()));
    }
    context.RequestCompleted();
}

Source: https://github.com/wj60387/WebApiOAUthBase/blob/master/OwinWebApiBase/WebApiOwinBase/Providers/OAuthServerProvider.cs

As for my remaining three questions:

1. Right now, anybody can request an authorization code, the client_id is ignored. ValidateClientAuthentication is apparently not hit as part of AuthorizeEndpoint. How do I obtain ClientId in AuthorizeEndpoint?

Answer: You have to implement `ValidateClientAuthentication'.

2. The authorization code is not coupled to a client. Anyone who intercepts the code could use it. How do I obtain the ClientId in AuthorizationCodeProvider.Create so that I can store it with the code?

Answer: OAuthAuthorizationServerProvider takes care of this. As long as you set "client_id" in the ticket, it will check that the client that requests an access token for the authorization code is the same.

3. The authorization code is not coupled to a user at all, it's an empty ClaimsIdentity. How do I put a user-login page in between and in AuthorizeEndpoint obtain the ClaimsIdentity for the logged-in user?

Answer: You create a separate login page. What this does is sign the user in. If your WebAPI uses cookie-based authentication, you can just redirect the user to the AuthorizeEndpoint again. If you use access tokens, your login page has to make a request to `AuthorizeEndpoint' with the access token to obtain an authorization code. (Don't give the access token to the third party. Your login page requests the authorization code and sends that back.) In other words, if you use access tokens then there are two clients involved in this flow.