Passing Trigger POST Body to CI script

Is there any way to pass the body of an HTTP POST from GitLab repo trigger into GitLab CI?

The background for this request stems from wishing to kick off automated test builds whenever a push or pull_request is made to an external GitHub repo. The GitHub Repo issues an HTTPS POST to an internal GitLab repo’s trigger endpoint. The trigger is able to successfully start scripts/builds via runners, but the runners are operating blind as to why they were kicked off. All of the info I really want is within the POST body, which I believe the trigger drops. Further, as far as I know, there is no way in GitHub to change the payload endpoint to incorporate variables.

And before you ask, due to corporate ID policies, I am not able to run my own internal web server to consume the GitHub HTTPS POST directly.

Thanks for any tips!