Anyone who really wants to contribute to the project (and scratch their itch) will not have a problem with entering a username, password, and perhaps use a validation link from an e-mail. It might discourage people with just fleeting interest.
And as a hypothetical FOSS project maintainer, I know I'd rather have one of the first kind of contributor than ten of the second kind. Especially if the alternative is to be beholden to the likes of Microsoft.
Of course, the best solution would be something like ForgeFed, but I can't see that meaningfully taking off (there's no way Github will ever adopt it). I'd love to be wrong, though.