def sign_out(authenticatable_class)
      key = cookie_name(authenticatable_class)
      cookies.encrypted.permanent[key] = {value: nil}
      cookies.delete(key)
      true
    end
def sign_out(authenticatable_class)
      key = cookie_name(authenticatable_class)
      cookies.encrypted.permanent[key] = {value: nil}
      cookies.delete(key)
      true
    end
Signs out user by deleting their encrypted cookie.
 @param (see #authenticate_by_cookie)
 @return [boolean] Always true