"Sign in as Different User" menu option is missing in SharePoint Server 2013

To work around this issue, use one of the following methods

1. Start Internet Explorer by using the Run as different user option, and then go to the SharePoint site.
   
   Note: The Run as different user option is visible if you hold the Shift key when you right-click a program icon.
2. Access the SharePoint site by using the the URL as http://siteurl/_layouts/closeConnection.aspx?loginasanotheruser=true
   
   Important:
   
   This option uses an unsupported browser feature which is unreliable and causes other issues. Currently this option does not work in IE 10 and Safari.