discourse/lib/auth/google_oauth2_authenticator.rb

class Auth::GoogleOAuth2Authenticator < Auth::Authenticator

  def name
    "google_oauth2"
  end

  def enabled?
    SiteSetting.enable_google_oauth2_logins
  end

  def description_for_user(user)
    info = GoogleUserInfo.find_by(user_id: user.id)
    info&.email || info&.name || ""
  end

  def can_revoke?
    true
  end

  def revoke(user, skip_remote: false)
    info = GoogleUserInfo.find_by(user_id: user.id)
    raise Discourse::NotFound if info.nil?

    # We get a temporary token from google upon login but do not need it, and do not store it.
    # Therefore we do not have any way to revoke the token automatically on google's end

    info.destroy!
    true
  end

  def can_connect_existing_user?
    true
  end

  def after_authenticate(auth_hash, existing_account: nil)
    session_info = parse_hash(auth_hash)
    google_hash = session_info[:google]

    result = ::Auth::Result.new
    result.email = session_info[:email]
    result.email_valid = session_info[:email_valid]
    result.name = session_info[:name]

    result.extra_data = google_hash

    user_info = ::GoogleUserInfo.find_by(google_user_id: google_hash[:google_user_id])

    if existing_account && (user_info.nil? || existing_account.id != user_info.user_id)
      user_info.destroy! if user_info
      result.user = existing_account
      user_info = GoogleUserInfo.create!({ user_id: result.user.id }.merge(google_hash))
    else
      result.user = user_info&.user
    end

    if !result.user && !result.email.blank? && result.email_valid
      result.user = User.find_by_email(result.email)
      if result.user
        # we've matched an existing user to this login attempt...
        if result.user.google_user_info && result.user.google_user_info.google_user_id != google_hash[:google_user_id]
          # but the user has changed the google account used to log in...
          if result.user.google_user_info.email != google_hash[:email]
            # the user changed their email, go ahead and scrub the old record
            result.user.google_user_info.destroy!
          else
            # same email address but different account? likely a takeover scenario
            result.failed = true
            result.failed_reason = I18n.t('errors.conflicting_google_user_id')
            return result
          end
        end
        ::GoogleUserInfo.create({ user_id: result.user.id }.merge(google_hash))
      end
    end

    result
  end

  def after_create_account(user, auth)
    data = auth[:extra_data]
    GoogleUserInfo.create({ user_id: user.id }.merge(data))
  end

  def register_middleware(omniauth)
    options = {
      setup: lambda { |env|
        strategy = env["omniauth.strategy"]
         strategy.options[:client_id] = SiteSetting.google_oauth2_client_id
         strategy.options[:client_secret] = SiteSetting.google_oauth2_client_secret
      },
      skip_jwt: true
    }

    if (google_oauth2_prompt = SiteSetting.google_oauth2_prompt).present?
      options[:prompt] = google_oauth2_prompt.gsub("|", " ")
    end

    google_oauth2_hd = SiteSetting.google_oauth2_hd
    options[:hd] = google_oauth2_hd if google_oauth2_hd.present?

    # jwt encoding is causing auth to fail in quite a few conditions
    # skipping
    omniauth.provider :google_oauth2, options
  end

  protected

  def parse_hash(hash)
    extra = hash[:extra][:raw_info]

    h = {}

    h[:email] = hash[:info][:email]
    h[:name] = hash[:info][:name]
    h[:email_valid] = extra[:email_verified]

    h[:google] = {
      google_user_id: hash[:uid] || extra[:sub],
      email: extra[:email],
      first_name: extra[:given_name],
      last_name: extra[:family_name],
      gender: extra[:gender],
      name: extra[:name],
      link: extra[:hd],
      profile_link: extra[:profile],
      picture: extra[:picture]
    }

    h
  end
end