> It seems a bit harsh to judge the strength of an authentication scheme on the metric of "How well does it stand up to a system administrator storing and serving publicly all in-use authentication credentials?"

Is it harsh? Would it be harsh to judge an authentication scheme that stores all passwords in plaintext? Server logs don't typically contain data that should be considered secret. IF this authentication scheme led to secret information being stored in a file that wasn't expected to be secure, that would be a major problem, wouldn't it?

This type of authentication hasn't stood up to a large amount of scrutiny, so it is important to think through some attack vectors that might be opened up. This was one I thought up, but it isn't an issue since the tokens are one-shot.

For the record, I like this authentication scheme but that doesn't mean it shouldn't be challenged.