🌩️ Use cloud caching

No need to use GitHub's action cache.

The credentials used here are intended to be used by third parties. That
is, they're safe to have in this workflow and may be copy-pasted into
any projects that would like to use NativeLink as remote cache.

.github/workflows/test-stdlib.yaml

@@ -18,6 +18,8 @@ jobs:
         os: [ubuntu-24.04]
     runs-on: ${{ matrix.os }}
     timeout-minutes: 60
+    permissions:
+      id-token: write
     steps:
 
       - name: Checkout
@@ -31,25 +33,36 @@ jobs:
       - name: Cache Nix derivations
         uses: >- # v6
           DeterminateSystems/magic-nix-cache-action@87e8236f46702ab0ce5a058b605a173ec88d618e
-      - name: Mount bazel cache
-        uses: >- # v4.0.2
-          actions/cache@0c45773b623bea8c8e75f6c82b208c3cf94ea4f9
+
+      - name: Get Web Identity Token via Cognito Identity Pool
+        id: web_id_token
+        # See: https://github.com/catnekaise/cognito-idpool-auth/issues/6
+        uses: >- # alpha
+          catnekaise/cognito-idpool-basic-auth@287d4dabb527d8b78d3df6e0436d46e3abd209d3
+        with:
+          cognito-identity-pool-id: >-
+            us-east-2:7edef192-7c1c-4e55-8ab4-6035b9c2288f
+          aws-account-id: 471112781046
+          aws-region: us-east-2
+          audience: sts.amazonaws.com
+
+      - name: Create secret from token
+        uses: actions/github-script@v6
         with:
-          path: |
-            ~/.cache/bazel
-          key: >-
-            ${{ runner.os }}-bazel-${{ hashFiles(
-              '.bazelversion',
-              '.bazelrc',
-              'MODULE.bazel',
-              'MODULE.bazel.lock',
-              '**/*.nix',
-              'flake.lock'
-            ) }}
-          restore-keys: |
-            ${{ runner.os }}-bazel-
+          # yamllint disable rule:line-length
+          script: >-
+            core.setSecret('NATIVELINK_TOKEN',
+            '${{ steps.web_id_token.outputs.cognito_identity_oidc_access_token }}')
 
       - name: Invoke Bazel build in Nix shell
+        env:
+          NATIVELINK_TOKEN: ${{ env.NATIVELINK_TOKEN }}
         run: |
           nix develop --impure --command \
-          bash -c "bazel test --jobs=4 @mojo//... --verbose_failures"
+          bash -c "bazel test \
+            --jobs=4 \
+            --verbose_failures \
+            --experimental_remote_cache_async \
+            --remote_header=x-nativelink-api-key=$NATIVELINK_TOKEN \
+            --remote_cache=grpcs://cas-gha-ci.build-faster.nativelink.net:443 \
+            @mojo//..."