# File lib/oauth2/access_token.rb, line 79
    def refresh!(params={})
      raise "A refresh_token is not available" unless refresh_token
      params.merge!(:client_id      => @client.id,
                    :client_secret  => @client.secret,
                    :grant_type     => 'refresh_token',
                    :refresh_token  => refresh_token)
      new_token = @client.get_token(params)
      new_token.options = options
      new_token
    end