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December 05, 2016

Managing Cookie Lifetime with ASP.NET Core OAuth 2.0 providers

I recently received a support request from a customer regarding the session lifetime once a user has signed in using Auth0 as they wanted the users to remain logged in across browser sessions. For our Auth0 integration with ASP.NET Core we have written no special middleware and instead rely on the standard OpenID Connect or OAuth2 middleware for authenticating users in MVC applications.

My initial response to the user was to simply configure the cookie middleware and specify an ExpireTimeSpan:

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    // ...

    app.UseCookieAuthentication(new CookieAuthenticationOptions
    {
        AutomaticAuthenticate = true,
        AutomaticChallenge = true,
        ExpireTimeSpan = TimeSpan.FromDays(7)
    });

    // ...
}

Turns out that does not do much. Even when specifying that option the cookie still only remains active for the duration for the session:

Cookie duration for lifetime of session only

Understanding what ASP.NET Core is doing

So I had a look at the Cookie Middleware documentation again and at the bottom of the document there is a section about “Persistent cookies and absolute expiry times”. It turns out that you have to specify the cookie persistence options when making a call to HttpContext.Authentication.SignInAsync(...).

The only catch with that is that when using only the OAuth 2.0 or OIDC middleware you never actually make the call to SignInAsync - instead the middleware does it for you automatically as can been seen in the source code for the RemoteAuthenticationHandler class - which is the base class for both the OAuthHandler and OpenIdConnectHandler classes of the OAuth 2.0 and OIDC middleware respectively.

Here is the relevant section of code of that class:

public abstract class RemoteAuthenticationHandler<TOptions> : AuthenticationHandler<TOptions> where TOptions : RemoteAuthenticationOptions
{
    protected virtual async Task<bool> HandleRemoteCallbackAsync()
    {
        // ...

        context.Properties.Items[AuthSchemeKey] = Options.AuthenticationScheme;

        await Options.Events.TicketReceived(context);

        if (context.HandledResponse)
        {
            Logger.SigninHandled();
            return true;
        }
        else if (context.Skipped)
        {
            Logger.SigninSkipped();
            return false;
        }

        await Context.Authentication.SignInAsync(Options.SignInScheme, context.Principal, context.Properties);

        // Default redirect path is the base path
        if (string.IsNullOrEmpty(context.ReturnUri))
        {
            context.ReturnUri = "/";
        }

        Response.Redirect(context.ReturnUri);
        return true;
    }
}

So once the authentication with the remote authentication handler has occurred, the user will be signed in with the SignInScheme of the relevant AuthenticationOptions instance. You usually specify this SignInScheme when you configure the authentication services in the ConfigureServices method of your Startup class, e.g.

public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthentication(options =>
    {
        options.SignInScheme = CookieAuthenticationDefaults.AuthenticationScheme;
    });

    // Add framework services.
    services.AddMvc();
}

The value of CookieAuthenticationDefaults.AuthenticationScheme is “Cookies”, which is the same default value which the Cookie Middleware uses when you register it using 

app.UseCookieAuthentication(new CookieAuthenticationOptions
{
    AutomaticAuthenticate = true,
    AutomaticChallenge = true
});

So that is how the OAuth 2.0 / OIDC middleware signs the user into using the cookie authentication middleware. That means that on every subsequent request the cookie middleware authenticates the user.

Option 1: Configuring the AuthenticationProperties in the OnTicketReceived event

When you look at the code of RemoteAuthenticationHandler which I linked to above, you will see that a few lines above the call to SignInAsync there is a call to Options.Events.TicketReceived() which will fire the OnTicketReceived event in our middleware.

Passed as a parameter to that even is an instance of TicketRecievedContext which contains a property of type AuthenticationProperties called Properties which is ultimately passed in the call to the SignInAsync which is what the ASP.NET Core documentation said is where we should configure the cookie persistence options.

So now with all that knowledge, all we really have to do is to handle the OnTicketReceived event when registering our OAuth 2.0 (or OIDC) middleware, and set the correct values to make the cookie persistent for 7 days:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    //...

    app.UseCookieAuthentication(new CookieAuthenticationOptions
    {
        AutomaticAuthenticate = true,
        AutomaticChallenge = true
    });

    app.UseGitHubAuthentication(new GitHubAuthenticationOptions
    {
        ClientId = "...",
        ClientSecret = "...",
        Scope = { "user:email" },
        Events = new OAuthEvents()
        {
            OnTicketReceived = context =>
            {
                context.Properties.IsPersistent = true;
                context.Properties.ExpiresUtc = DateTimeOffset.UtcNow.AddDays(7);

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

    // ...
}

And with that in place, when a user signs in to my application you can see that the cookie is now set to expire in 7 days (this blog post was written on 5 December 2016):

Cookie expires in 7 days

Option 2: Call SignInAsync ourselves in the OnTicketReceived

Looking at the source code for RemoteAuthenticationHandler again, there is another option which becomes evident. You will notice that there is an if statement which checks whether the HandledResponse property of the TicketRecievedContext was set when the OnTicketReceived event was handled. This suggest that we can in fact handle the sign in ourselves and then just indicate that we have done so.

Here is how we would do that:

app.UseGitHubAuthentication(new GitHubAuthenticationOptions
{
    ClientId = "...",
    ClientSecret = "...",
    Scope = { "user:email" },
    Events = new OAuthEvents()
    {
        OnTicketReceived = context =>
        {
            // Sign the user in ourselves
            context.HttpContext.Authentication.SignInAsync(context.Options.SignInScheme, context.Principal,
                new AuthenticationProperties
                {
                    IsPersistent = true,
                    ExpiresUtc = DateTimeOffset.UtcNow.AddDays(7)
                });

            // Indicate that we handled the login
            context.HandleResponse();

            // Default redirect path is the base path
            if (string.IsNullOrEmpty(context.ReturnUri))
            {
                context.ReturnUri = "/";
            }

            context.Response.Redirect(context.ReturnUri);

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

Notice in the code above that if you want to go this route you will also be responsible for redirecting the user onwards after you have signed them in.

Option 3: Storing remote authentication details in 2nd cookie

There is a 3rd option, and that is the route which ASP.NET Identity takes. It has 2 cookies, namely a “main” cookie which authenticates the user, and a second, intermediate cookie in which the user’s information is stored when they sign in using an external login provider such as any of the OAuth 2.0 or OIDC proviers.

Here is the basic priniciples of how this approach will work:

  1. 2 sets of cookie middleware is registered

    • One which is the “main” cookie (let’s call this one the Application Cookie) and which is the one that authenticates the user (AutomaticAuthenticate and AutomaticChallenge is set to true)
    • A second, temporary cookie (we’ll call this one the Remote Authentication Cookie) in which the login information received from the OAuth 2.0 provider will be stored
  2. The “default” SignInScheme for authentication will be set to the Remote Authentication Cookie. This means that the OAuth 2.0 middleware will sign in to the Remote Authentication Cookie and NOT the Application Cookie
  3. When the OAuth 2.0 middleware is challenged, we’ll instruct it to redirect to a new RemoteLoginCallback action after the user has authenticated with the OAuth 2.0 provider.
  4. This RemoteLoginCallback action will retrieve the user’s information from the Remote Authentication Cookie, and if it is successful it will manually sign the user in to the Application Cookie by making a call to HttpContext.Authentication.SignInAsync.

So in this version, this is my abbreviated Startup class:

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddAuthentication(options =>
        {
            options.SignInScheme = "RemoteAuthCookie";
        });

        // Add framework services.
        services.AddMvc();
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        //...
            
        app.UseCookieAuthentication(new CookieAuthenticationOptions
        {
            AuthenticationScheme = "RemoteAuthCookie",
            CookieName = "RemoteAuthCookie",
            AutomaticAuthenticate = false
        });

        app.UseCookieAuthentication(new CookieAuthenticationOptions
        {
            AuthenticationScheme = "ApplicationCookie",
            CookieName = "ApplicationCookie",
            AutomaticAuthenticate = true,
            AutomaticChallenge = true
        });

        app.UseGitHubAuthentication(new GitHubAuthenticationOptions
        {
            ClientId = "e31c9807a8ce042118d2",
            ClientSecret = "d8b883e189c7b6a1874e14f6d73c11d606b53d24",
            Scope = { "user:email" }
        });

        app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "default",
                template: "{controller=Home}/{action=Index}/{id?}");
        });
    }
}

And this is the AccountController class which handles logging the user in by challenging the OAuth 2.0 middleware, logging the user out, and also handling the callback from the OAuth 2.0 middleware which signs the user in to the main Application Cookie.

public class AccountController : Controller
{
    public async Task<IActionResult> Login()
    {
        // Construct the redirect url to go to the RemoteLoginCallback action
        var redirectUrl = Url.Action("RemoteLoginCallback", "Account", new { ReturnUrl = "/" });

        // Ensure we are signed out of the remote cookie auth
        await HttpContext.Authentication.SignOutAsync("RemoteAuthCookie");

        // Challenge the GH provider
        return new ChallengeResult("GitHub", new AuthenticationProperties() { RedirectUri = redirectUrl });
    }

    public IActionResult Logout()
    {
        HttpContext.Authentication.SignOutAsync("GitHub");
        HttpContext.Authentication.SignOutAsync("ApplicationCookie");

        return RedirectToAction("Index", "Home");
    }

    public async Task<IActionResult> RemoteLoginCallback(string returnUrl)
    {
        var auth = new AuthenticateContext("RemoteAuthCookie");

        // Get auth ticket from remote cookie
        await HttpContext.Authentication.AuthenticateAsync(auth);

        if (auth.Accepted)
        {
            // Sign out of remote cookie once we used it
            await HttpContext.Authentication.SignOutAsync("RemoteAuthCookie");

            // Sign the user in
            await HttpContext.Authentication.SignInAsync("ApplicationCookie", auth.Principal, new AuthenticationProperties
            {
                IsPersistent = true,
                ExpiresUtc = DateTimeOffset.UtcNow.AddDays(7)
            });

            return RedirectToLocal(returnUrl);
        }
        else
        {
            // If we don't have an external auth cookie, redirect to login action
            return RedirectToAction(nameof(Login));
        }

    }

    private IActionResult RedirectToLocal(string returnUrl)
    {
        if (Url.IsLocalUrl(returnUrl))
        {
            return Redirect(returnUrl);
        }
        else
        {
            return RedirectToAction(nameof(HomeController.Index), "Home");
        }
    }
}

Please note that the official ASP.NET Identity code does some extra checks for XSRF, so do not assume my code is “production ready”. If you want to go with this approach please reference the ASP.NET Identity source code, and especially the code for the GetExternalLoginInfoAsync method which read the user’s information from the external cookie.

Source code

You can find full source code demonstrating all 3 different approaches at https://github.com/jerriepelser-blog/oauth-authentication-cookies

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