in src/main/java/software/amazon/qldb/Session.java [95:105]
static Session startSession(String ledgerName, QldbSessionClient client) {
final StartSessionRequest request = StartSessionRequest.builder().ledgerName(ledgerName).build();
final SendCommandRequest command = SendCommandRequest.builder().startSession(request).build();
logger.debug("Sending start session request: {}", command);
final SendCommandResponse result = client.sendCommand(command);
final String sessionToken = result.startSession().sessionToken();
final String sessionId = result.responseMetadata().requestId();
return new Session(ledgerName, sessionToken, sessionId, client);
}