Unable to upload sourcemaps from Next.js project via GitHub Actions/Docker

[SheaBelsky]

I'm struggling to set up my Sentry project, and automatic sourcemap uploading, with a project that currently builds and pushes to a Docker image registry via GitHub Actions. I can do this from my local machine just fine, but as soon as I try to build via GitHub Actions, it fails to build and returns the following error:

#8 95.03 Sentry CLI Plugin: Command failed: /build-prod/node_modules/@sentry/cli/sentry-cli releases new IVsRIVe5vy7npsnGkot7P
#8 95.03 error: API request failed
#8 95.03   caused by: sentry reported an error: Authentication credentials were not provided. (http status: 401)

I have tried the following:

• Exposing SENTRY_AUTH_TOKEN as an environment variable
• Using mathieu-bour/setup-sentry-cli@1.2.0 to configure the CLI in advance of it actually being used
• Using getsentry/action-release@v1 to set up a release, although I don't think this actually does anything with sourcemaps.

The documentation doesn't cover how sourcemap uploading from CI/CD is intended to work. Am I meant to upload sourcemaps from my local machine first, and then disable Next.js sourcemap uploading at the CI/CD level? How do others configure automatic sourcemap uploading in a CI/CD environment for their projects? It isn't working for me, and I'm not sure if I'm missing a step in the documentation or if I'm going down a path that is not recommended.

I'm following these instructions after having used the wizard to set up some files automatically: https://docs.sentry.io/platforms/javascript/guides/nextjs