How to debug GitHub Action failure - ffmpeg

Question

Just yesterday a stable GitHub Action (CI) started failing rather cryptically and I've run out of tools to debug it.
All I can think of is our BUNDLE_ACCESS_TOKEN went bad somehow but I didn't set that up. It's an Action secret under Repository Secrets that are not visible in GitHub UI. How can I test to see if it's valid?
Or maybe it's something else?!? "Bad credentials" is vague...
Here's the meat of the action we're trying to run:
#my_tests.yml
jobs:
my-test:
runs-on: ubuntu-latest
services:
postgres:
image: postgres:13.4
env:
POSTGRES_USERNAME: postgres
POSTGRES_PASSWORD: postgres
POSTGRES_DB: myapp_test
ports:
- 5432:5432
options: --health-cmd pg_isready --health-interval 10s --health-timeout 5s --health-retries 5
env:
RAILS_ENV: test
POSTGRES_HOST: localhost
POSTGRES_USERNAME: pg
POSTGRES_PASSWORD: pg
GITHUB_TOKEN: ${{ secrets.BUNDLE_ACCESS_TOKEN }}
BUNDLE_GITHUB__COM: x-access-token:${{ secrets.BUNDLE_ACCESS_TOKEN }}
CUCUMBER_FORMAT: progress
steps:
- uses: actions/checkout#v2
- uses: FedericoCarboni/setup-ffmpeg#v1
...
And with debug turned on here's the Failure (line 20) from GitHub Actions:
Run FedericoCarboni/setup-ffmpeg#v1
1 ------- ##[debug]Evaluating condition for step: 'Run FedericoCarboni/setup-ffmpeg#v1'
2 ##[debug]Evaluating: success()
3 ##[debug]Evaluating success:
4 ##[debug]=> true
5 ##[debug]Result: true
6 ##[debug]Starting: Run FedericoCarboni/setup-ffmpeg#v1
7 ##[debug]Loading inputs
8 ##[debug]Loading env
9 Run FedericoCarboni/setup-ffmpeg#v1
10 with:
11 env:
12 RAILS_ENV: test
13 POSTGRES_HOST: localhost
14 POSTGRES_USERNAME: pg
15 POSTGRES_PASSWORD: pg
16 GITHUB_TOKEN: ***
17 BUNDLE_GITHUB__COM: x-access-token:***
19 CUCUMBER_FORMAT: progress
20 Error: Bad credentials
21 ##[debug]Node Action run completed with exit code 1
22 ##[debug]Finishing: Run FedericoCarboni/setup-ffmpeg#v1
Thanks for any help.

Answer 1

For your particular case try scoping GITHUB_TOKEN and BUNDLE_GITHUB__COM only to steps that actually use it instead the whole job.
Also consider switching to FedericoCarboni/setup-ffmpeg#v2 it has built in support for github.token.
Generic GH Action Debugging
https://github.com/nektos/act
Run actions locally. Mostly gives you faster feedback for experiments.
https://github.com/mxschmitt/action-tmate
Allows you to create interactive remote session where you can poke around.