code: public void sendRequest(String username, String servicename,
  			String methodname, byte[] requestdata) throws SshException {
  
  		ByteArrayWriter msg = new ByteArrayWriter();
  		try {
  
  			msg.write(SSH_MSG_USERAUTH_REQUEST);
  			msg.writeString(username);
  			msg.writeString(servicename);
  			msg.writeString(methodname);
  			if (requestdata != null) {
  				msg.write(requestdata);
  			}
  
  			transport.sendMessage(msg.toByteArray(), true);
  		} catch (IOException ex) {
  			throw new SshException(ex, SshException.INTERNAL_ERROR);
  		} finally {
  			try {
  				msg.close();
  			} catch (IOException e) {
  			}
  		}
  	}
docs: Send an authentication request. This sends an SSH_MSG_USERAUTH_REQUEST
  message.
  
  @param username
  @param servicename
  @param methodname
  @param requestdata
  the request data as defined by the authentication
  specification
  @throws SshException