startTls method
Upgrades the current insure connection to SSL.
Opportunistic TLS (Transport Layer Security) refers to extensions in plain text communication protocols, which offer a way to upgrade a plain text connection to an encrypted (TLS or SSL) connection instead of using a separate port for encrypted communication.
Implementation
Future<void> startTls() async {
await sendCommand(PopStartTlsCommand());
log('STTL: upgrading socket to secure one...', initial: 'A');
await upradeToSslSocket();
}