Asynchronously performs a TLS handshake on conn. See gio.tls_connection.TlsConnection.handshake for more information.
the [I/O priority][io-priority] of the request
a #GCancellable, or null
callback to call when the handshake is complete
Asynchronously performs a TLS handshake on conn. See gio.tls_connection.TlsConnection.handshake for more information.