feat: Add npm builder workflow

.github/actions/checkout-node/action.yml

@@ -0,0 +1,65 @@
+name: "Checkout a repository for a Node project"
+description: "Checkout and setup the environment for a Node project"
+inputs:
+  repository:
+    description: "Repository name with owner."
+    required: false
+    # Same default as https://github.com/actions/checkout/blob/main/action.yml#L6.
+    default: ${{ github.repository }}
+  ref:
+    # Note: the logic is fairly involved https://github.com/actions/checkout/blob/main/src/ref-helper.ts,
+    # so we do not attempt to resolve it ourselves or provide a default value. We let the official `actions/checkout`
+    # do it for us.
+    description: "The branch, tag or SHA to checkout."
+    required: false
+  token:
+    description: "The token to use."
+    required: false
+    # Same default as https://github.com/actions/checkout/blob/main/action.yml#L24.
+    default: ${{ github.token }}
+  node-version:
+    description: "The Node version to use, as expected by https://github.com/actions/setup-node."
+    required: true
+
+runs:
+  using: "composite"
+  steps:
+    # Note: we could use a single block:
+    #  `uses: actions/checkout
+    #     with:
+    #       ref: "${{ inputs.ref }}"`
+    # and it would work, because the ref field does not have a default
+    # value set https://github.com/actions/checkout/blob/main/action.yml#L7-L11.
+    # However, if this were to change in the future, we'd be setting an empty value
+    # when the developer has not defined it; and it would overwrite the default value
+    # set by the `actions/checkout`. Even if it is highly unlikely the `actions/checkout` team
+    # will set a default value in the future, we want to be sure it does not affect us if they do.
+    # This is why we use 2 blocks to call the `actions/checkout`:
+    #   1. if inputs.ref != ''
+    #   2. if inputs.ref == ''
+    - name: Checkout the repository with user ref
+      if: inputs.ref != ''
+      uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+      with:
+        fetch-depth: 1
+        persist-credentials: false
+        repository: "${{ inputs.repository }}"
+        ref: "${{ inputs.ref }}"
+        token: "${{ inputs.token }}"
+
+    - name: Checkout the repository with default ref
+      if: inputs.ref == ''
+      uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+      with:
+        fetch-depth: 1
+        persist-credentials: false
+        repository: "${{ inputs.repository }}"
+        token: "${{ inputs.token }}"
+
+    - name: Verify checkout
+      uses: slsa-framework/slsa-github-generator/.github/actions/verify-checkout@e3220805577deb9d193f64e519abcb3b50851df5
+
+    - name: Set up Node environment
+      uses: actions/setup-node@2fddd8803e2f5c9604345a0b591c3020ee971a93 # tag=v3.4.1
+      with:
+        node-version: "${{ inputs.node-version }}"

.github/workflows/builder_go_slsa3.yml

@@ -24,6 +24,10 @@ env:
   BUILDER_BINARY: slsa-builder-go-linux-amd64 # Name of the binary in the release assets.
   BUILDER_DIR: internal/builders/go # Source directory if we compile the builder.
 
+defaults:
+  run:
+    shell: bash
+
 ###################################################################
 #                                                                 #
 #            Input and output argument definitions                #
@@ -156,7 +160,6 @@ jobs:
 
       - name: Build dry project
         id: build-dry
-        shell: bash
         env:
           CONFIG_FILE: "${{ inputs.config-file }}"
           UNTRUSTED_ENVS: "${{ inputs.evaluated-envs }}"
@@ -195,7 +198,6 @@ jobs:
       - name: Download dependencies
         env:
           UNTRUSTED_WORKING_DIR: "${{ needs.build-dry.outputs.go-working-dir }}"
-        shell: bash
         run: |
           set -euo pipefail
 
@@ -211,7 +213,6 @@ jobs:
 
       - name: Build project
         id: build-gen
-        shell: bash
         env:
           CONFIG_FILE: "${{ inputs.config-file }}"
           UNTRUSTED_ENVS: "${{ inputs.evaluated-envs }}"
@@ -262,7 +263,6 @@ jobs:
 
       - name: Create and sign provenance
         id: sign-prov
-        shell: bash
         env:
           UNTRUSTED_BINARY_NAME: "${{ needs.build-dry.outputs.go-binary-name }}"
           UNTRUSTED_BINARY_HASH: "${{ needs.build.outputs.go-binary-sha256 }}"