This catches `NoMethodError`'s that are thrown in two cases. The first case is when `password=` isn't defined on the subject (probably didn't call `has_secure_password`). The second case is when `password_digest=` isn't defined on the subject (probably didn't add a `password_digest` column to schema). Both cases are rescued from here and handled by setting a reasonable failure message instead of tossing the exception to the caller.