sqlauth is a simple package for managing user authentication that is backed by a database. Emphatically, this package does not handle login forms or redirections. It only exposes a few functions for managing user passwords and authenticating a user's password.

go get github.com/BurntSushi/sqlauth

This package is emphatically in BETA. Although most of the API is determined by the gorilla/sessions package, there are still some pieces that may need some changing. (For example, to allow key rotation.)