ssl://
URLs are quite specific to PHP. It's the way PHP provides a way to use a direct SSL/TLS connection when using its fsocketopen
function. See List of Supported Socket Transports in the manual.
ssl://
will give you an SSL/TLS connection without any application protocol on top of it: it will be up to your application to implement whichever protocol you require for the communication.
In contrast, https://
will implement the HTTP protocol over this SSL/TLS connection.
Note that the default settings for ssl://
and tls://
are rather poor in terms of security. In particular, the default value for verify_peer
is false, which would make the connection vulnerable to MITM attacks.