Google Analytics Browser Cookie

Question

I have a contact form on a Wordpress website.

When a lead is submitted, I want to capture the Google Analytics ClientID (stored in the _ga cookie in the browser) as part of the submission.

Using this ClientID, I want to interrogate the Google Analytics Reporting API for the first session user activity linked to this lead, fetching the data linked to the following variables:

• Source

• Medium

• Campaign Name

• Campaign Content

• Campaign Term

• Search Query

This is the first time working with the GA API.

Any help would be appreciated.