One workaround here would be to move the update site to an unprotected but obscurely named folder, like
https://devstudio.jboss.com/updates/4.0-SDSDFHLIK23I487IDSFKLWDRUWREF12389DFILANSDD387AO8S7DAS4O8A7SDAKL7ELAW7483LA7
then rather than publish the URL, we give people a zip, like the one attached.
To get updates, they'd manually add the zip via Help > Install new software > Add > Archive > browse for the zip.
This would give them the URL of the site, but buried in a zip file we could put in the CSP. No typing, no passwords, etc.
Only drawback is that the /updates/4.0/ URL would therefore be empty.
In future, we could look at a plugin in JBDS that could somehow resolve credentials from the CSP and use that to get a per-user update site URL which they could use.
Similar to the contents of the zip, we would GENERATE a folder like http://access.redhat.com/whatever/something/something/nboldt@redhat.com/jbds/4.0/updates/ which would contain the composite metadata pointing at the real location of the site.
This is as secure as having a public registration form to get the username/password, in that it could be just as easily blogged/shared and therefore circumvented.
Password has been removed from http://devstudio.jboss.com/updates/4.0/