"no username" trips authentication dialogue

A nephew has emailed us a wedding invitation in the form of a website.
It requires a password, which he tells us in the email, but does NOT
require a username.

With Netsurf, the site starts loading, then the "Site Authentication"
dialogue pops up asking for Username and Password. Leave the first
field blank, type the password, click Login, loading apparently
continues, then the Site Authentication dialogue pops up again
(showing blank and password just as we left it).

I tried on an Android browser. Its dialogue shows only a Password
field, no field for username, and it displays without problem.

Seems strange if the RiscOS authentication routine has never come
across this situation before. Netsurf #4204.

--
Jim Nagel www.archivemag.co.uk