In the previous note, Gavin gives the technical reasons why it would be difficult to authenticate proctors (as opposed to students) via LDAP. Since I don't understand these technical details, I'm not in a position to say whether or not it's worth the effort to try to fix this flaw.
But if a fix is impractical, let me suggest something that might be easier.
First let me say why I care. We were administering gateway exams for the first time this semester, and found that no proctor could authenticate anyone. Nor could any professor. The only proctors who had any power were those set up as dummy accounts for testing purposes, since these accounts had passwords that were supplied manually, rather than through LDAP. Diagnosing the problem took many hours, even though we had a WW expert on call. While the situation is documented correctly at the bottom of this page, it also seems reasonable to me that no one here noticed it. So I'm not sure how we, or any other school in our shoes, could have avoided experiencing this problem.
Anyway, here's a potential partial-fix: When a proctor tries to authorize someone to take a test, and WW cannot find any password for that proctor, and WW knows that LDAP is in use, perhaps it could give a more informative message than that the proctor’s authentication failed. Perhaps append the following to the usual error message. "Note: LDAP authentication is not available for proctors, who must have a manually supplied password."
Is this feasible?