Web API + Service API + Cookie Auth Gotcha

I ran into an interesting problem while on a past project this year - when we turned on Service API via OWIN, my authorized Web API endpoints were returning a 401. We were using cookie authentication for the Web API endpoints. This baffled me a bit until I peeled back the code for Service API.

When one of the Service API's initialization modules executes, it bypasses the default host authentication by calling SupportDefaultHostAuthentication on the Global HTTP Configuration. This explains why my API endpoints weren't recognizing the logged in user's cookie. I came up with a workaround that ignored this call and used cookie authentication instead. See below - during this project, we were using Episerver 10.9.1, and Service API 3.0.1:

Add the following code to your OWIN startup. This code ultimately re-adds cookie auth to the Web API filter pipeline

GlobalConfiguration.Configuration.Filters.Add(new HostAuthenticationFilter(DefaultAuthenticationTypes.ApplicationCookie));

In your API controller, decorate your controller or action with the System.Web.Http's Authorize Attribute

After I made these changes, I was able to access my authorized Web API endpoints. As a quick note, if you do use cookie authentication for your Web API endpoints, you may want to send an antiforgery token to protect against XSRF attacks. In this project, I sent the antiforgery token as a header and created a filter attribute that validated the token against the logged in user's cookie. In case anyone is interested, here was my setup:

In my master layout, I included a global antiforgery token. I placed this right after the <body> tag, but you can place this anywhere.
In my client side code, I sent the antiforgery token as a header. I called the __RequestVerificationToken.

On the server side, I created an attribute called UserValidateAntiForgeryTokenAttribute that inherited from FilterAttribute and IAuthorizationFilter. In the ExecuteAuthorizationFilterAsync method, I grabbed the cookie and token values and validated them against each other.

public Task<HttpResponseMessage> ExecuteAuthorizationFilterAsync(HttpActionContext actionContext,
            CancellationToken cancellationToken, Func<Task<HttpResponseMessage>> continuation)
        {
            try
            {
                // get headers
                var headers = actionContext.Request.Headers;

                // get cookie value
                var cookieRvtValue = headers
                    .GetCookies()
                    .Select(c => c[AntiForgeryConfig.CookieName])
                    .FirstOrDefault()
                    ?.Value;

                // get header value
                var headerRvtValue = headers.GetValues("__RequestVerificationToken").FirstOrDefault();

                // validate
                AntiForgery.Validate(cookieRvtValue, headerRvtValue);
            }
            catch
            {
                actionContext.Response = new HttpResponseMessage
                {
                    StatusCode = HttpStatusCode.Forbidden,
                    RequestMessage = actionContext.ControllerContext.Request
                };
                var source = new TaskCompletionSource<HttpResponseMessage>();
                source.SetResult(result);
                return source.Task;
            }
            return continuation();
        }
    }

Decorate your Web API controller action with the attribute

[UserValidateAntiForgeryToken]
[Authorize]
[HttpGet]
public string DoGetAction()
{
     // do something
     return string.empty;
}

Thanks for reading. Hope you find this helpful!

Dec 18, 2017

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