SharePoint 2013: Sign in as Different User

SharePoint 2013 does not include the ability to log in as another user...and this sometimes could be painful.

There are several solutions to this problem:

1. Start your browser as a different user
2. Use the _layouts/closeConnection.aspx?loginasanotheruser=true page
3. Add a link to _layouts/closeConnection.aspx?loginasanotheruser=true page either in master page or in the left menu of page that you need to modify adding a security trimmed control in order to render this link only to certain users. For this purpose see Security Trimmed Control
4. Edit the Welcome.aspx to include the link again (Sign in as Different User and SharePoint 2013)
5. Use JavaScript as a Bookmarklet (SharePoint 2013 – Sign in as Another User)

I do not suggest the third option: the customization of the layouts pages is not the best solution and it is not safe in case of updates on the server farm (like configuration of service pack, etc).
Moreover, this link cannot be trimmed and probably this functionality have to be avoided to certain users.

My advice is to use other solutions such as the 2, 3 or 5.
For more information, please read the official MSDN article about this problem: "Sign in as Different User" menu option is missing in SharePoint Server 2013. 

Enjoy!

AC