Returns the TLS session data or undefined if no session was negotiated. On the client, the data can be provided to the session option of connect to resume the connection. On the server, it may be useful for debugging.
See Session Resumption for more information.
Note: getSession() works only for TLSv1.2 and below. For TLSv1.3, applications must use the 'session' event (it also works for TLSv1.2 and below).