All Authenticated Users in SP10

To get claim for All Authenticated Users in PS you need to use:

$claim = New-SPClaimsPrincipal -EncodedClaim "c:0(.s|true"

for windows users (NT AUTHORITY\authenticated users):

$claim = New-SPClaimsPrincipal -EncodedClaim "c:0!.s|windows"

and for all forms authenticated users (basic asp.net membership provider)

 $claim = New-SPClaimsPrincipal -EncodedClaim "c:0!.s|forms:aspnetsqlmembershipprovider"