Enable Claims based authentication on an existing web application in SharePoint

When you provision a web application in SharePoint 2010 you get the option to enable Claims based authentication. However, after the provisioning there's no option in the GUI to turn it on. PowerShell saves the day again with the option to change from classic to claims based authentication using the lines below.

$WebAppName = "http://test:8001"
$account = "Administrator" 
$wa = get-SPWebApplication $WebAppName
Set-SPwebApplication $wa –AuthenticationProvider (New-SPAuthenticationProvider) 

–Zone Default

The user running these command should be a member of the SharePoint_Shell_Access role on the config DB, and a member of the WSS_ADMIN_WPG local group.