class Devise::Strategies::Rememberable

def authenticate!

strategy handle the authentication.
the record in the database. If the attempt fails, we pass to another
To authenticate a user we deserialize the cookie and attempt finding 
def authenticate!
  resource = mapping.to.serialize_from_cookie(*remember_cookie)
  unless resource
    cookies.delete(remember_key)
    return pass
  end
  if validate(resource)
    success!(resource)
  end
end