Fix missing variable declarations in auth backends.
Review Request #6672 — Created Dec. 2, 2014 and submitted
The auth backends were attempting to decode UTF-8 username strings into byte strings before operating on them, in order to convert them to a format expected by the libraries providing authentication. If a byte string is passed in, though, the variables are never declared, causing errors. This fixes this case, adding the missing variable declarations.
No testing, just a visual inspection. Unit tests pass, for what it's worth.