In an svn project where hudson's security is setup as "Matrix-based security",
"Trigger builds remotely (e.g., from scripts)" does not work, even with with a
specified "Authentication Token" UNLESS Anonymous "Read" has been selected in
Hudson's Authorization.

This is undocumented. I'd enable "Read" access for the Anonymous user, but
there is a security issue in that an Anonymous user with "Read" access can tag a
build release when viewing a particular build.

Cheers,
Kevin