Refresh Google OAuth2 access token

google_auth_service.rb

class GoogleAuthService
  def initialize(identity)
    @identity = identity
    @oauth2_token = @identity.token
    @oauth2_refresh_token = @identity.refresh_token
  end

  def refresh_token!
    new_token = token.refresh!

    @identity.update(
      token: new_token.token,
      refresh_token: new_token.refresh_token,
      expires_at: Time.at(new_token.expires_at)
    ) unless new_token.expired?
  end

  private

  def strategy
    OmniAuth::Strategies::GoogleOauth2.new(
      nil,
      ENV['GOOGLE_CLIENT_ID'],
      ENV['GOOGLE_CLIENT_SECRET']
    )
  end

  def client
    strategy.client
  end

  def token
    OAuth2::AccessToken.new(
      client,
      @oauth2_token,
      refresh_token: @oauth2_refresh_token
    )
  end
end

identity.rb

# == Schema Information
#
# Table name: identities
#
#  id            :integer          not null, primary key
#  provider      :string
#  uid           :string
#  user_id       :integer
#  created_at    :datetime         not null
#  updated_at    :datetime         not null
#  profile_link  :string
#  token         :string
#  refresh_token :string
#  expires_at    :integer
#

class Identity < ActiveRecord::Base
  belongs_to :user

  validates :provider, :user_id, :uid, presence: true

  def self.find_from_omniauth(auth)
    find_by(provider: auth.provider, uid: auth.uid)
  end

  def self.create_from_omniauth(auth, user)
    if auth.provider == 'facebook'
      profile_link = 'https://facebook.com/' + auth.uid
    else
      profile_link = auth.info.try(:urls).try(:first).try(:[], 1)
    end

    Identity.create!(user: user,
                     provider: auth.provider,
                     uid: auth.uid,
                     profile_link: profile_link,
                     token: auth.credentials.token,
                     refresh_token: auth.credentials.refresh_token,
                     expires_at: auth.credentials.expires_at)
  end

  def expired?
    expires_at.present? && expires_at < Time.now.to_i
  end
end

static_pages_controller.rb

class StaticPagesController < ApplicationController
  before_action :check_google_token

  # ...
  
  private

  def check_google_token
    if current_user.identity.expired?
      GoogleAuthService.new(current_user.identity).refresh_token!
    end
  end
end