Overrides AuthenticatorInterface::authenticate
https://www.ietf.org/rfc/rfc4954.txt
public function authenticate(EsmtpTransport $client) : void { $client->executeCommand(\sprintf("AUTH PLAIN %s\r\n", base64_encode($client->getUsername() . \chr(0) . $client->getUsername() . \chr(0) . $client->getPassword())), [ 235, ]); }