Google API OAuth 2.0 refresh token (Ruby on Rails)

token.rb

# The OAuth access token provided by the Google API expires in 60 minutes. After expiration,
# you must exchange a refresh token for a new access token. Unfortunately, the the Google API 
# ruby gem does not include a method for refreshing access tokens. 

# You can read up on how to refresh an access token here: 
# https://developers.google.com/accounts/docs/OAuth2WebServer#refresh

# This Token model implements that process. It's based off of a Token model that can be created 
# by running: 
# rails g model Token token:text refresh_token:string expires_at:datetime

# This code assumes you Google API CLIENT_ID and CLIENT_SECRET are set as environment variables. 

# Google only sends the refresh token the first time you authorize your account. 
# If you didn't save it, go to your Gmail Account Permissions and revoke permissions to your app

class Token < ActiveRecord::Base

  def to_params
    { 'refresh_token' => refresh_token,
      'client_id'     => ENV['CLIENT_ID'],
      'client_secret' => ENV['CLIENT_SECRET'],
      'grant_type'    => 'refresh_token'}
  end

  def request_token_from_google
    url = URI("https://accounts.google.com/o/oauth2/token")
    Net::HTTP.post_form(url, self.to_params)
  end

  def refresh!
    data = JSON.parse(request_token_from_google.body)
    update_attributes(
      token: data['access_token'],
      expires_at: Time.now + data['expires_in'].to_i.seconds
    )
  end
  
  def self.access_token
    #convenience method to retrieve the latest token and refresh if necessary
    t = Token.last
    t.refresh! if t.expires_at < Time.now
    t.token
  end

end