Experiment with GitHub Actions: log in to gcloud.

.github/workflows/build.yml

@@ -0,0 +1,32 @@
+name: build
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+  workflow_dispatch:
+
+jobs:
+
+  ubuntu:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        include:
+          - { CC: gcc, CXX: g++ }
+          - { CC: clang, CXX: clang++ }
+
+    steps:
+      - name: Set up Cloud SDK
+        uses: google-github-actions/setup-gcloud@master
+        with:
+          project_id: ${{ secrets.GCP_PROJECT_ID }}
+          service_account_key: ${{ secrets.GCP_SA_KEY }}
+          export_default_credentials: true
+      
+      - name: Use gcloud CLI
+        run: gcloud info