External Social Login/Authentication with Microsoft ASP.NET Identity Does Not Work

Well, it's painful as hell, when you spend many days developing custom implementation of ASP.NET Identity with a main goal to enable social/external authentication (as in Facebook, Google, Twitter, etc.) and at the end everything works but the social authentication itself.

The main reason of it not working is that inside ExternalLogin (or similarly named) action method of an Account controller the external login info object is always null:

      var info = await AuthenticationManager.GetExternalLoginInfoAsync();
      if (info == null)
      {
         return RedirectToAction("Login");
      }

Google search returns a lot of discussions on Stack Overflow and it takes a lot of time to go through them but eventually you'll find out (and will be very disappointed) that if you did everything right with your Identity implementation and did not make any stupid mishaps than it's totally not your fault and there is almost nothing in answers on Stack Overflow for you to figure out the problem.

Apparently it's an OWIN bug that is still not fixed (I tested with both Identity 2.0.x and 2.1 and it's still there and happening) as it was figured by smart people (https://stackoverflow.com/questions/20737578/asp-net-sessionid-owin-cookies-do-not-send-to-browser) and without going into obscure details there is a simple fix for it.

In a Login (or named similarly) action method (GET version) of your Account controller add the very first line of code as below:

      Session["dummy"] = "dummy";

The most disappointing part of this problem is that it will not necessarily surface while you are testing. First everything might work just fine and than suddenly out of thin air without any obvious reason it will stop working completely. If it's the case (you had it working and than it stopped) than this is your solution: just add that dummy code line as above and it will do the magic.

Let's see how long it will take Microsoft to fix this bug. Happy coding and thanks all the smart people for sharing their findings.

Cheat Sheet for Enabling Output Caching in ASP.NET MVC

What is Output Caching

ASP.NET output caching feature allows increasing web application performance by returning content that was built some time ago instead of rebuilding it on every request. Returning content from cache only takes a few milliseconds as opposed to executing a full request cycle that could take much longer.
The content is being cached on the ASP.NET level and the request would not reach the application code for the content that is still in cache. ASP.NET output caching can be used in both WebForms and MVC applications and using it in MVC has become even easier than before.

When to use Output Caching

Output caching is useful when content returned by a controller action method does not change frequently, requires more than few CPU cycles or database access and does not require a lot of memory to store. For example, I would not recommend to use output caching for a large binary object like an image or a file. Also there is no point to cache a short string that only takes a few milliseconds to build. The best use case would be an average size content that requires some calculation or database access to produce but does not change on every request.

How to enable Output Caching

The easiest way to enable output caching in MVC is using an OutputCache attribute on the controller or controller action method. Applying output caching on a controller action method is recommended as it gives much better granularity and control over output caching. The best way to control output caching behaviour is via caching profiles that allow defining all parameters in a web.config file and override them for each environment where the web application is deployed (i.e. Dev, QA, Stage, Live, etc.)

Limitations

ASP.NET MVC has some limitations for output caching, for example: caching profile is not supported for a partial/child controller method therefore caching parameters including Duration and VaryByParam must be set in the code.

Implementation and code review check points

1. Apply to individual action methods
2. Use Caching profiles
3. Partial/child action methods should not be cached for too long
4. Disable output caching in Dev/QA/Stage environment.
5. Do not forget to set Duration and VaryByParam values in web.config

Example

<system.web>
  <caching>
    <outputcachesettings>
      <outputcacheprofiles>
        <add name="cacheProfile" duration="60" varyByParam="*" />
      </outputCacheProfiles>
    </outputCacheSettings>
  </caching>
</system.web>

[OutputCache(CacheProfile = "cacheProfile")]
public ActionResult Test()
{
    ViewData["result"] = "This text was rendered at " + DateTime.Now;
    return View();
}

Setting Cache Control HTTP Headers in Web API Controller Method

Controlling caching behaviour of an HTTP response is an important task that cannot be ignored as it will have a big impact on a web application load and performance. In ASP.NET Web Forms and MVC applications it usually is done by using special directives or attributes that take care of adding corresponding headers to the response. ASP.NET Web API framework unfortunately does not come with an out of the box support for this functionality so concious developers need to deal with that themselves. Luckily it is not a difficult task to do as the Web API framework has a number of support objects that simplify the job.

Basically in order to control caching behaviour we need to make sure that the output response will have what is called "Cache control header" with proper values that determine caching behaviour. Example below demonstrates how to make a response publicly cacheable for a period of time:

   var response = new HttpResponseMessage();
   response.Headers.CacheControl = new CacheControlHeaderValue
          {Public = true, MaxAge = TimeSpan.FromSeconds(maxAge)};

To simplify the usage further we can even create a static extension method that can be easily applied in a controller method:

// somewhere in a static class
public static HttpResponseMessage PublicCache(this HttpResponseMessage response, int maxAge)
{
   response.Headers.CacheControl = new CacheControlHeaderValue
          {Public = true, MaxAge = TimeSpan.FromSeconds(maxAge)};
   return response;
}
...
// inside an ApiController class
public HttpResponseMessage MyApiMethod(long id)
{
   var response = new HttpResponseMessage();
   ..............
   return response.PublicCache(24 * 7 * 60);
}

Setting a "Content-Disposition" HTTP Header in Web API Controller Method

When developing an ASP.NET Web API controller method that allows to download a file it is considered a good practice to set a "Content-Disposition" header to guide a browser of a name of a file being downloaded.

There are two different ways to approach this simple task. First is to add a new HTTP header to the HTTP response using string values for the header's name and value. The second is to try and use the .NET framework's infrastructure methods that presumably should make this task easier.

The first method seems to be very simple but potentially dangerous: one would need to hard-code string values and be totally responsible for the values to be properly formatted according to the W3C standards.

var response = new HttpResponseMessage();
response.Headers.Add("Content-Disposition", "attachment; filename=fileName.ext");

The second method is to try and delegate handling of the specifics of the HTTP protocol to the .NET framework by using corresponding presumably built-in methods. This seems more appropriate and even easier to achieve. However due to poor documentation of the Web API extensions that is easier said than done. without further ado this is how it's done:

var response = new HttpResponseMessage();
response.Content.Headers.ContentDisposition = 
   new ContentDispositionHeaderValue("attachment") { FileName = fileName};

Only one string value here should hard-coded with a guideline available in the official documentation so it's not that bad.

If you find this information possible share it with your fellow colleagues so it may save their valuable time.

Using jQuery to Consume ASP.NET MVC JSON Services

Since the inception of ASP.NET Web Services have been an important part of any professional web developer's tool set. Starting .NET 3.5 Web Services became even more useful as it became possible to call Web Services asynchronously from a browser using JavaScript and ASP.NET AJAX.

However for the last two years the alternative ASP.NET MVC framework has been drawing more and more attention from the development community due to its good implementation of the MVC design pattern and adherence to web standards and bleeding edge web technologies.

For many experienced ASP.NET developers accustomed to Web Services especially accompanied with ASP.NET AJAX framework a natural question occurs: how to implement similar approach with ASP.NET MVC framework and its natural JavaScript companion jQuery?