On the menu command on SharePoint 2013 there is no longer “Sign in as Different User”.
This menu item is very useful when testing applications, but according to Microsoft, it can lead to problems especially when opening document, say in Microsoft Word. So, it maybe for these reasons that the option has been removed in SharePoint 2013.
You can add the menu item back in, but recommend only to do this in a development / test environment. To do this, repeat this edit on all servers in your SharePoint farm.
- 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” and then save the file.
<SharePoint:MenuItemTemplate runat="server" ID="ID_LoginAsDifferentUser" Text="<%$Resources:wss,personalactions_loginasdifferentuser%>" Description="<%$Resources:wss,personalactions_loginasdifferentuserdescription%>" MenuGroupId="100" Sequence="100" UseShortId="true"/>
Now when you view the drop down menu “Sign in as Different User” will be there.