private function getSslProtocol(){
		$version = $this->readEnvironmentVariable(self::ENVIRONMENT_VARIABLE_SSL_VERSION);
		$rs = null;
		switch ($version) {
			case self::SSL_VERSION_SSLV2:
				$rs = 'sslv2';
				break;
			case self::SSL_VERSION_SSLV3:
				$rs = 'sslv3';
				break;
			case self::SSL_VERSION_TLSV1:
				$rs = 'tls';
				break;
			case self::SSL_VERSION_TLSV11:
				$rs = 'tlsv1.1';
				break;
			case self::SSL_VERSION_TLSV12:
				$rs = 'tlsv1.2';
				break;
			default:
				$rs = 'ssl';
		}
		if ($rs === null) {
			throw new \Exception("Invalid state.");
		}

		$possibleTransportProtocols = stream_get_transports();
		if (!in_array($rs, $possibleTransportProtocols)) {
			throw new \Exception("The enforced SSL protocol is '" . $rs . "'. But this protocol is not supported by the web server. Supported stream protocols by the web server are " . implode(', ', $possibleTransportProtocols) . ".");
		}

		return $rs;
	}