“Sign in as different user” option in SharePoint 2013

We can do it in two ways.

First way:

Just type the url : http://siteurl/_layouts/closeConnection.aspx?loginasanotheruser=true

Second way:

In your sharepoint server installed Server:

1. Go to path: C:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\TEMPLATE\CONTROLTEMPLATES
2. In that file you will find Welcome.ascx file.
3. Open the file with Notepad and add the below code exactly before the tag.ID_RequestAcess
4. 
5. Just Refresh after the change is done.