Testcafe native browser dialog not displaying, getNativeDialogHistory is undefined

I'm just getting started with testcafe. The website that I need to test has a native browser window alert that loads before anything displays on the page, and that alert prompts the user for credentials. If the cancel button is clicked, the page is blank except for one word "unauthorized".

When I have my test navigate to this website, I see no window alert at all. The page immediately displays the "unauthorized" message. Is testcafe automatically closing this alert? Neither setNativeDialogHandler nor getNativeDialogHistory are working. How can I have testcafe enter text into two fields in this dialog?

Thank you!