code: public Supplier<Connection> getConnectionSupplier() {
          final boolean startConnection = isStartConnection();
  
          if (connectionSupplier == null) {
              if (getUserName() == null) {
                  connectionSupplier = () -> {
                      try {
                          final Connection connection = getConnectionFactory().createConnection();
                          if (startConnection) {
                              connection.start();
                          }
                          return connection;
                      } catch (JMSException e) {
                          throw new JmsNotConnectedException("Unable to create context", e);
                      }
                  };
              } else {
                  final String userName = getUserName();
                  final String password = getPassword();
  
                  connectionSupplier = () -> {
                      try {
                          final Connection connection = getConnectionFactory().createConnection(userName, password);
                          if (startConnection) {
                              connection.start();
                          }
                          return connection;
                      } catch (JMSException e) {
                          throw new JmsNotConnectedException("Unable to create context for user " + userName, e);
                      }
                  };
              }
          }
          return connectionSupplier;
      }
docs: If the user name is set, use the user name and password to create the JMS connection.
  
  @return connection supplier
  @see JmsServiceBuilder#connectionSupplier