Add GHA Docker build

Author: goffrie

.github/workflows/ci.yml

@@ -0,0 +1,30 @@
+# based on https://docs.github.com/en/packages/managing-github-packages-using-github-actions-workflows/publishing-and-installing-a-package-with-github-actions
+name: GHCR push
+env:
+  IMAGE_NAME: traefik-forward-auth
+on:
+  push:
+    tags:
+      - v*
+jobs:
+  push:
+    runs-on: ubuntu-24.04-arm
+    permissions:
+      packages: write
+      contents: read
+    steps:
+      - uses: actions/checkout@v4
+      - name: Build image
+        run: docker build . --file Dockerfile.arm64 --tag $IMAGE_NAME --label "runnumber=${GITHUB_RUN_ID}"
+      - name: Log in to registry
+        run: echo "${{ secrets.GITHUB_TOKEN }}" | docker login ghcr.io -u ${{ github.actor }} --password-stdin
+      - name: Push image
+        run: |
+          IMAGE_ID=ghcr.io/${{ github.repository_owner }}/$IMAGE_NAME
+          IMAGE_ID=$(echo $IMAGE_ID | tr '[A-Z]' '[a-z]')
+          VERSION=$(echo "${{ github.ref }}" | sed -e 's,.*/\(.*\),\1,')
+          [[ "${{ github.ref }}" == "refs/tags/"* ]] && VERSION=$(echo $VERSION | sed -e 's/^v//')
+          echo IMAGE_ID=$IMAGE_ID
+          echo VERSION=$VERSION
+          docker tag $IMAGE_NAME $IMAGE_ID:$VERSION
+          docker push $IMAGE_ID:$VERSION