define ssh_user ($ssh_key){

    user { $name: ensure=>present ...... }
    ssh_authorized_key{$name: key=>$ssh_key, ensure=>present, user=>$name,  require=>User[$name]}

}

@ssh_user{"barnaclebob": ssh_key=>"asdfasdfasdfasdf"}
@ssh_user{"greenman": ssh_key=>"foobarbaz"}


realize Ssh_user["greenman"]