What you are running into is called BASIC web server authentication. While searching on SO there are a number of similar questions that have been asked over time. This particular one is nice as it has several solution approaches that can be tried.
As the popup is technically not part of the page's DOM, this can not be addressed using xpath. There are roughly two approaches:
- Fill in the text boxes using a key stroke simulator like SendKeys.
- Prevent the popup from appearing.
In this case you're already on your way for the second one. By including the username and password in the url, the popup is prevented. The following Robot Script uses that example to access a local page that is secured by basic authentication using this tutorial.
*** Settings ***
Library Selenium2Library
*** Test Cases ***
Test Chrome
Create Webdriver Chrome
Go To http://admin:admin@localhost:8090/basic-auth/
Capture Page Screenshot
[Teardown] Close All Browsers
As the popup is prevented, there is no need separately input the username and password.