# File lib/omniauth/strategy.rb, line 464
    def fail!(message_key, exception = nil)
      env['omniauth.error'] = exception
      env['omniauth.error.type'] = message_key.to_sym
      env['omniauth.error.strategy'] = self

      if exception
        log :error, "Authentication failure! #{message_key}: #{exception.class}, #{exception.message}"
      else
        log :error, "Authentication failure! #{message_key} encountered."
      end

      OmniAuth.config.on_failure.call(env)
    end