Missing "Sign in as Different User" option in sharepoint 2013
If you are using this menu option in previous versions of sharepoint, there is no link for "Sign in as Different User" anymore...
But there is 2 workarounds for having the same functionality;
1. Change the siteurl with yours and it will ask you for the new username and password
2. Open internet explorer by using "run as different user" option (Shift+ right click) by entering the username and password that you like
Keep in mind first option may not work in some browsers and ie10