Problem with oauth2 service account authentication (Ruby)

Hi there, I'm currently developing a web application using rails where one of the modules uses Adwords API data such as keyword search volume and CPC. Here's a short flow of the process:

The user creates a campaign and add in seeder keywords/keywords and the web application will get the adwords api data for the keywords. 

Problem is, I'm having a very hard time in authenticating the service account and making calls to get data from the api. I have tried using the googleauth gem using the information provided on its page but it was quite confusing for me and didn't work out in the end. I have also tried following this method in Step 3 which uses the old 0.8.x version of google-api-client and didn't work out either.

Is there a guide or simpler way of getting authenticated and the api data? Would appreciate it anyone could help :)

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