AngularJS Web Api AntiForgeryToken CSRF

Add to the ASP.NET MVC View that serves the AngularJS SPA, let's say Views\Home\Index.cshtml, the HTML helper that generates the AntiForgeryToken.

@Html.AntiForgeryToken();

Configure AngularJS to pass the above generated AntiForgeryToken as Request Header.

angular.module('app')
.run(function ($http) {
    $http.defaults.headers.common['X-XSRF-Token'] =
        angular.element('input[name="__RequestVerificationToken"]').attr('value');
});

Create a custom Web API Filter to validate all non-GET requests (PUT, PATCH, POST, DELETE).

This assumes that all your GET requests are safe and don't need protecting.
If that's not the case, remove the if (actionContext.Request.Method.Method != "GET") exclusion.

using System;
using System.Linq;
using System.Net.Http;
using System.Web.Helpers;
using System.Web.Http.Filters;

namespace Care.Web.Filters
{
    public sealed class WebApiValidateAntiForgeryTokenAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(
            System.Web.Http.Controllers.HttpActionContext actionContext)
        {
            if (actionContext == null)
            {
                throw new ArgumentNullException("actionContext");
            }

            if (actionContext.Request.Method.Method != "GET")
            {
                var headers = actionContext.Request.Headers;
                var tokenCookie = headers
                    .GetCookies()
                    .Select(c => c[AntiForgeryConfig.CookieName])
                    .FirstOrDefault();

                var tokenHeader = string.Empty;
                if (headers.Contains("X-XSRF-Token"))
                {
                    tokenHeader = headers.GetValues("X-XSRF-Token").FirstOrDefault();
                }

                AntiForgery.Validate(
                    tokenCookie != null ? tokenCookie.Value : null, tokenHeader);
            }

            base.OnActionExecuting(actionContext);
        }
    }
}

Register the newly created filter as a global one, in Global.asax.cs.

    private static void RegisterWebApiFilters(HttpFilterCollection filters)
    {
        filters.Add(new WebApiValidateAntiForgeryTokenAttribute());
    }

Alternatively, if you don't wish to add this filter globally, you can put it only on certain Web API actions, like this

[WebApiValidateAntiForgeryToken]

This, of course, is by definition less secure, as there's always the chance that you'll forget to apply the attribute to an action that needs it.

Also, note that you must have the Microsoft.AspNet.WebApi.Core package in order to have access to System.Web.Http namespace. You can install it via NuGet with Install-Package Microsoft.AspNet.WebApi.Core.

This post has been heavily inspired by this blog post.