Authorization_code grant flow on Owin.Security.OAuth: returns invalid_grant

Question

I am trying to setup my authentication using the authorization_code grant flow. I had it previously working with grant_type=password, so I kind of know how the stuff is supposed to work. But when using grant_type=authorization_code, I couldn't make it return anything other than invalid_grant

Here is my setup:

app.UseOAuthAuthorizationServer(new OAuthAuthorizationServerOptions
{
    AllowInsecureHttp = true,
    TokenEndpointPath = new PathString("/auth/token"),
    AccessTokenExpireTimeSpan = TimeSpan.FromMinutes(5),
    Provider = new SampleAuthProvider()
});

app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions
{
    AuthenticationMode = Microsoft.Owin.Security.AuthenticationMode.Active,
    AuthenticationType = "Bearer"
});

SampleAuthProvider is the following class: https://gist.github.com/anonymous/8a0079b705423b406c00

Basically, it's just logging every step and validating it. I tried the request:

POST http://localhost:12345/auth/token
grant_type=authorization_code&code=xxxxxx&client_id=xxxxx&redirect_uri=https://xxxx.com/
Content-Type: application/x-www-form-urlencoded

It's going through:

• OnMatchEndpoint
• OnValidateClientAuthentication

And that's all. I expected it to call OnValidateTokenRequest and OnGrantAuthorizationCodenext, but it just didn't. I have no idea why.

The xxxx's in the request aren't placeholders, I tried it like that. Maybe the middleware makes some checks on its own and rejects the request because of that? I tried variants of the redirect_uri with http, without any protocol, without trailing slash...

It also works properly with a custom grant_type. It so if I too desperate, I guess I can use that to simulate authorization_code, but I'd rather not have to do that.

TL;DR

My OAuthAuthorizationServerProvider returns {"error":"invalid_grant"}after OnValidateClientAuthentication when using grant_type=authorization_code.

• Why is it stopping there?
• How can I make the whole damn thing work?

Thanks for your help!

---

Edit

As pointed out by RajeshKannan, I made a mistake in my configuration. I didn't provide an AuthorizationCodeProvider instance. However, that didn't completely solve the problem, since in my case, the code is not issued by the AuthorizationCodeProvider, and I can't just deserialize it. I anwered with the workaround I got working.

Answer 1

Here is what I got working. I'm not completely comfortable with that solution, but it works and should help others to fix their issues.

---

So, the issue is that I didn't set the AuthorizationCodeProvider property. When a request with grant_type=authorization_code is received, the code must be validated by that code provider. The framework assumes that the code was issued by that code provider, but that's not my case. I get it from another server and have to send the code back to it for validation.

In the standard case, where you are also the one issuing the code, the link provided by RajeshKannan describes everything you have to do.

Here is where you have to set the property:

app.UseOAuthAuthorizationServer(new OAuthAuthorizationServerOptions
{
    TokenEndpointPath = new PathString(Paths.TokenPath),
    Provider = new SampleAuthProvider(),
    AuthorizationCodeProvider = new MyAuthorizationCodeProvider ()
}

And the declaration of the MyAuthorizationCodeProvider class:

internal class MyAuthorizationCodeProvider : AuthenticationTokenProvider
{
    public override async Task ReceiveAsync(
        AuthenticationTokenReceiveContext context)
    {
        object form;
        // Definitely doesn't feel right
        context.OwinContext.Environment.TryGetValue(
                "Microsoft.Owin.Form#collection", out form); 
        var redirectUris = (form as FormCollection).GetValues("redirect_uri");
        var clientIds = (form as FormCollection).GetValues("client_id");
        if (redirectUris != null && clientIds != null)
        {
            // Queries the external server to validate the token
            string username = await MySsoService.GetUserName(context.Token,
                                                             redirectUris[0]);
            if (!string.IsNullOrEmpty(username))
            {
                var identity = new ClaimsIdentity(new List<Claim>()
                {
                    // I need the username in  GrantAuthorizationCode
                    new Claim(ClaimTypes.NameIdentifier, username) 
                }, DefaultAuthenticationTypes.ExternalBearer);

                var authProps = new AuthenticationProperties();

                // Required. The request is rejected if it's not provided
                authProps.Dictionary.Add("client_id", clientIds[0]); 

                // Required, must be in the future
                authProps.ExpiresUtc = DateTimeOffset.Now.AddMinutes(1); 

                var ticket = new AuthenticationTicket(identity, authProps);
                context.SetTicket(ticket);
            }
        }
    }
}