Sign in as a Different User in SharePoint 2013

By default in SharePoint 2013 there is no option for "Sign in as different user".

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.

Following the below mentioned steps you can enable this option in SharePoint 2013.

Solution

Step: 1
Go to the location C:\Program Files\Common Files\microsoft shared\Web ServerExtensions\15\TEMPLATE\CONTROLTEMPLATES.
Here we have a file named welcome.ascx.


We need to edit this file to enable the option.

Step: 2
Open welcome.ascx in Visual Studio or in Notepad and add the following code and save:

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<SharePoint:MenuItemTemplate runat="server" ID="ID_LoginAsDifferentUser"
  Text="<%$Resources:wss,personalactions_loginasdifferentuser%>"
  Description="<%$Resources:wss,personalactions_loginasdifferentuserdescription%>"
  MenuGroupId="100"
  Sequence="100"
  UseShortId="true"
  />

And it should be above the tag which has ID_RequestAcess.

Step: 3
Refresh the site, and it's been enabled:


Source: http://www.codeproject.com/Tips/684751/How-to-enable-Sign-in-as-different-user-option-in