What should I do when on Azure Web Role I get "HTTP Error 401.2 - Unauthorized. You are not authorized to view this page due to invalid authentication headers"

This post is dedicated to a simple but annoying issue that can appear when you are developing a ASP.NET MVC Application.

When I run my web application on my local machine, directly from Visual Studio, my web sites works perfectly. When I deploy it on a Web Role I get "HTTP Error 401.2 - Unauthorized. You are not authorized to view this page due to invalid authentication headers"

The same problem can appears if you deploy on on-premises servers, but in general this problem pop-ups on Web Roles. Not because a web role is different (it has the same layers as a web server -OS and IIS), but because people that are working with cloud solutions forget about infrastructure layers.

If we are reading the error message we can identify some possible root causes. But basically it seems that the user that is trying to access the page is not authorized.
But why it is working on the development machine from Visual Studio? Simple, in general the developer is also the admin on the machine and he access the page as an administrator and has full access.
On the local machine this can be replicated easily if you deploy the web site on your local IIS and play a little with the user that access the web site.

If you will not set this value, the value that is set in IIS will be used by default. For web roles, by default IIS is 'closed', it means that it is not open for anonymous access and you need to specify if you want to allow anonymous users to access your website.
Based on what Visual Studio template you are using to create your web site, the value could be set by default to true or not.

To allow anonymous users to access your web site you need to do the following things in the configuration file (web.config):

<system.web>
     <authorization>
          <allow users="*" />
     </authorization>
</system.web>
...
<system.webServer>
     <security>
          <authorization>
               <add accessType="Allow" users="?" />
          </authorization>
     </security>
</system.webServer>

The above configuration disables all authentication mechanisms and allows anonymous users to access your site.

For HTTP error code 401.2 on Web Roles I observed that this is the most common problem.