How To: Allow users to sign_in using their username or email address - heartcombo/devise GitHub Wiki
Note: this is a duplicate of https://github.com/plataformatec/devise/wiki/How-To:-Allow-users-to-sign-in-using-their-username-or-email-address
Note: this is a duplicate of https://github.com/plataformatec/devise/wiki/How-To:-Allow-users-to-sign-in-using-their-username-or-email-address