Q:

How to handle the grant_type error with the google_drive gem?

I'm trying to use the Ruby gem 'google_drive'. Before using that gem, I'm obtaining the user's token via the gem omniauth-google-oauth2.
When I try to use google_drive as follows:
  def google_oauth2(current_user)

    session = GoogleDrive.login_with_oauth(self.token)

    # Gets list of remote files.
    session.files.each do |file|
      p file.title
    end
  end 

I get the following error:
Sending HTTP get https://www.googleapis.com/drive/v3/files?fields=%2A
Caught error Authorization failed.  Server message:
{
 "error": "invalid_request",
 "error_description": "Required parameter is missing: grant_type"
}
Error - #<Signet::AuthorizationError: Authorization failed.  Server message:
{
 "error": "invalid_request",
 "error_description": "Required parameter is missing: grant_type"
}>

Completed 500 Internal Server Error in 128ms (ActiveRecord: 0.4ms)

How can I resolve this?
Update
Omniauth code being used to store the google oauth 2 tokens:
  def google_oauth2
    auth_hash = request.env['omniauth.auth']

    @authentication = Authentication.find_or_create_by(
                                            user_id: current_user.id,
                                            provider: auth_hash["provider"],
                                            uid: auth_hash["uid"]
                                          )
    @authentication.update_attributes(
                                      :token => auth_hash['credentials']['token'],
                                      :refresh_token => auth_hash['credentials']['refresh_token'],
                                      :provider_description => auth_hash["info"].email
                                    )

    flash[:notice] = "google_oauth2 authed."
    redirect_to '/'
  end

A:

Working solution to access google drive api without requiring a config.json. This solution uses the refresh token obtained from the google auth 2 omniauth strategy:
  require 'google/apis/drive_v2'
    auth = Signet::OAuth2::Client.new(
      token_credential_uri: 'https://accounts.google.com/o/oauth2/token',
      client_id:            "XXX-XXX",
      client_secret:        "XXX",
      refresh_token:        self.refresh_token # Get this from the omniauth strategy. 
    )

    auth.fetch_access_token!

    x = Google::Apis::DriveV2
    drive = x::DriveService.new
    drive.authorization = auth

files = drive.list_files

This took me .5 day. I hope it helps someone else out there! :)

