lowercasify username on login request
When a user registers, the chosen username is lowercased before being stored to the database. When a user attempts to log in, the supplied username is passed through as it was typed, which may contain uppercase letters. A user who registered his or her name using uppercase letters may not realize that the username was lowercased internally and may continue trying to log in with uppercase letters.
After a failed login attempt with uppercase letters, the login form helpfully displays the username lowercased. However, it still may not be clear to the end user that he or she needs to log in with that lowercased username.