SharePoint 2013 sign in as another user

• Locate the file \15\TEMPLATE\CONTROLTEMPLATES\Welcome.ascx and open in a text editor.
• Add the following element before the existing element with the id of “ID_RequestAccess”:

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

Save the file