Replace Cosign with GitHub native attestation (#141)

No longer double signing.

Signed-off-by: Bradley Reynolds <[email protected]>

.github/workflows/container-build-push.yaml

@@ -26,18 +26,11 @@ jobs:
     permissions:
       contents: read
       packages: write
-      # This is used to complete the identity challenge
-      # with sigstore/fulcio.
-      id-token: write
       # Used by actions/attest-build-provenance
+      id-token: write
       attestations: write
 
     steps:
-      - name: "Install cosign"
-        uses: sigstore/cosign-installer@59acb6260d9c0ba8f4a2f9d9b48431a222b68e20 # v3.5.0
-        with:
-          cosign-release: "v1.13.6"
-
       - name: "Setup Docker buildx"
         uses: docker/setup-buildx-action@988b5a0280414f521da01fcc63a27aeeb4b104db # v3.6.1
 
@@ -71,19 +64,6 @@ jobs:
           cache-from: type=gha
           cache-to: type=gha,mode=max
 
-      # Sign the resulting Docker image digest.
-      # This will only write to the public Rekor transparency log when the Docker
-      # repository is public to avoid leaking data.  If you would like to publish
-      # transparency data even for private images, pass --force to cosign below.
-      # https://github.com/sigstore/cosign
-      - name: "Sign the published Docker image"
-        if: ${{ inputs.push }}
-        env:
-          COSIGN_EXPERIMENTAL: "true"
-        # This step uses the identity token to provision an ephemeral certificate
-        # against the sigstore community Fulcio instance.
-        run: cosign sign ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}@${{ steps.build-and-push.outputs.digest }}
-
       - name: Generate artifact attestation
         if: ${{ inputs.push }}
         uses: actions/attest-build-provenance@210c1913531870065f03ce1f9440dd87bc0938cd # v1.4.0