Ruby AdWords API returning AuthenticationError.OAUTH_TOKEN_HEADER_INVALID

Have someone worked with Google AdWords API ?

I’m using

  • devise
  • omniauth
  • omniauth-google-oauth2
  • google-adwords-api
    I’m getting the token from oauth callback:
class OmniauthCallbacksController < Devise::OmniauthCallbacksController
  def google_oauth2
session[:token] = request.env["omniauth.auth"].    credentials
...
  end
end

and following the example of adwords on rails to get api instance:

 def adwords_api
@api ||= create_adwords_api
end

 def create_adwords_api
api = AdwordsApi::Api.new Rails.application.config_for(:adwords)

   token = session[:token]
   if token
credentials = api.     credential_handler
credentials.set_credential :oauth2_token, token
credentials.set_credential :client_customer_id, current_user.   id
end
   api
end

but when I try to get campaigns, It returns an error: [AuthenticationError.OAUTH_TOKEN_HEADER_INVALID @ ; trigger:'<null>'

and based on the log, this is the url of request:
[2015-01-09T10:12:44.237172 #6481] DEBUG -- : SOAP request: https://adwords.google.com/api/adwords/cm/v201409/CampaignService

How can I fix this?