Use PHP to do the webhook of GitHub, as follows:
$cmd = "eval `ssh-agent -s` && ssh-add && cd $target && git pull 2>&1";
$res = shell_exec($cmd);
SSH key (no password) has been added. No error is returned, but it is not successful.
$CMD = "CD $target & & git pull 2 > & 1"; will prompt no permission, because the key should not be loaded.