Using secrets with GitHub Actions

In the following example uses and exposes the GITHUB_TOKEN secretopen_in_new as provided by GitHub in your workflow.

First, create a Dockerfile that uses the secret:

# syntax=docker/dockerfile:1
FROM alpine
RUN --mount=type=secret,id=github_token \
  cat /run/secrets/github_token

In this example, the secret name is github_token. The following workflow exposes this secret using the secrets input:

name: ci

on:
  push:
    branches:
      - "main"

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v4
      - name: Set up QEMU
        uses: docker/setup-qemu-action@v3
      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3
      - name: Build
        uses: docker/build-push-action@v5
        with:
          context: .
          platforms: linux/amd64,linux/arm64
          tags: user/app:latest
          secrets: |
            "github_token=${{ secrets.GITHUB_TOKEN }}"

Note
You can also expose a secret file to the build with the secret-files input:
secret-files: |
  "MY_SECRET=./secret.txt"  

If you're using GitHub secretsopen_in_new and need to handle multi-line value, you will need to place the key-value pair between quotes:

secrets: |
  "MYSECRET=${{ secrets.GPG_KEY }}"
  GIT_AUTH_TOKEN=abcdefghi,jklmno=0123456789
  "MYSECRET=aaaaaaaa
  bbbbbbb
  ccccccccc"
  FOO=bar
  "EMPTYLINE=aaaa

  bbbb
  ccc"
  "JSON_SECRET={""key1"":""value1"",""key2"":""value2""}"

Key	Value
`MYSECRET`	`***********************`
`GIT_AUTH_TOKEN`	`abcdefghi,jklmno=0123456789`
`MYSECRET`	`aaaaaaaa\nbbbbbbb\nccccccccc`
`FOO`	`bar`
`EMPTYLINE`	`aaaa\n\nbbbb\nccc`
`JSON_SECRET`	`{"key1":"value1","key2":"value2"}`

Note
Double escapes are needed for quote signs.