I started creating some code based upon this for sending push notifications from PHP.
However now that I have understood there is a new API which utilizes HTTP/2 and
yes, it's possible:
$errno=0;$errstr="";
$sock = stream_socket_client(
"api.push.apple.com:443",
$errno,
$errstr,
4,
STREAM_CLIENT_CONNECT,
stream_context_create(["ssl" => ["local_cert" => "/path/to/cert.pem","verify_peer"=>false,"verify_peer_name"=>false]])
);
stream_socket_enable_crypto($sock, true, STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT);