If you’re ever in need of converting your existing web applications within SharePoint to claims authentication from classic auth, you’ll need to run the following commands.

In order to do this, you’ll need to use the SharePoint PowerShell command prompt and run the commands in the order below under your farm service account:

$WebAppName = “http://yourwebapp.contoso.com”
$account = “Contoso\contoso-farm-acct”
$wa = get-SPWebApplication $WebAppName
Set-SPwebApplication $wa -AuthenticationProvider (New-SPAuthenticationProvider) -Zone Default

(after the above command, entered Yes as Y and hit enter)

$account = (New-SPClaimsPrincipal -identity $account -identitytype 1).ToEncodedString()
$zp = $wa.ZonePolicies(“Default”)
$p = $zp.Add($account,”PSPolicy”)
$fc=$wa.PolicyRoles.GetSpecialRole(“FullControl”)
$p.PolicyRoleBindings.Add($fc)
$wa.Update()
$wa = get-SPWebApplication $WebAppName
$wa.MigrateUsers($true)

$wa.ProvisionGlobally()