fix: remove unused service and redundant IAM bindings in workload identity setup script (#481)

The original fix for
#444 dated
in January is incomplete.

This change removes an unused Google internal service
`cloudcode-pa.googleapis.com` for users in the setup script for Workload
Identity Federation.

It also removes redundant IAM bindings on the Workload Identity Pool's
principal in Step 4. These IAM bindings are added in Step 5 on a
connected service account to the Workload Identity Pool, different from
its principal. GitHub Actions "impersonates" this connected service
account, which has access to Google Cloud resources and services.

Lastly, it updates the description to correctly reflect the content of
the shell script.

I have published this
[codelab](https://codelabs.developers.google.com/gemini-cli/gemini-cli-security-review#0)
that teaches about this setup.

Signed-off-by: Tianzi Cai <tianzi@google.com>

Author: anguillanneuf

scripts/setup_workload_identity.sh

@@ -15,10 +15,12 @@
 # limitations under the License.
 
 # Universal Direct Workload Identity Federation Setup Script for GitHub Actions
-# This script sets up Google Cloud Direct Workload Identity Federation for any GitHub repository
-# to work with the google-github-actions/auth action.
+# The original script sets up Google Cloud Direct Workload Identity Federation for
+# any GitHub repositorty to work with the google-github-actions/auth action.
 # 
-# Uses Direct WIF (preferred): No intermediate service accounts, direct authentication to GCP resources.
+# It has been modified for Gemini CLI, which requires a special WIF setup
+# setup through a Service Account.
+
 
 set -e
 
@@ -221,9 +223,7 @@ required_apis=(
 )
 # Separately enable the internal-only Cloud Code API, ignoring errors
 # for public users who may not have access.
-gcloud services enable "cloudcode-pa.googleapis.com" --project="${GOOGLE_CLOUD_PROJECT}" || true
 gcloud services enable "${required_apis[@]}" --project="${GOOGLE_CLOUD_PROJECT}"
-gcloud services enable "cloudcode-pa.googleapis.com" --project="${GOOGLE_CLOUD_PROJECT}" || true
 print_success "APIs enabled successfully."
 
 # Step 2: Create Workload Identity Pool
@@ -319,38 +319,10 @@ else
 fi
 
 # Step 4: Grant required permissions to the Workload Identity Pool
-print_header "Step 4: Granting required permissions to Workload Identity Pool"
+print_header "(Skipped) Step 4: Granting required permissions to Workload Identity Pool"
 PRINCIPAL_SET="principalSet://iam.googleapis.com/${WIF_POOL_ID}/attribute.repository/${GITHUB_REPO}"
 
-print_info "Granting required permissions directly to the Workload Identity Pool..."
-
-# Observability permissions
-print_info "Granting logging permissions..."
-gcloud projects add-iam-policy-binding "${GOOGLE_CLOUD_PROJECT}" \
-    --role="roles/logging.logWriter" \
-    --member="${PRINCIPAL_SET}" \
-    --condition=None
-
-print_info "Granting monitoring permissions..."
-gcloud projects add-iam-policy-binding "${GOOGLE_CLOUD_PROJECT}" \
-    --role="roles/monitoring.metricWriter" \
-    --member="${PRINCIPAL_SET}" \
-    --condition=None
-
-print_info "Granting tracing permissions..."
-gcloud projects add-iam-policy-binding "${GOOGLE_CLOUD_PROJECT}" \
-    --role="roles/cloudtrace.agent" \
-    --member="${PRINCIPAL_SET}" \
-    --condition=None
-
-# Model inference permissions
-print_info "Granting vertex permissions..."
-gcloud projects add-iam-policy-binding "${GOOGLE_CLOUD_PROJECT}" \
-    --role="roles/aiplatform.user" \
-    --member="${PRINCIPAL_SET}" \
-    --condition=None
-
-print_success "Required permissions granted to Workload Identity Pool"
+print_info "(Skipped) Granting required permissions directly to the Workload Identity Pool..."
 
 # Step 5: Create and Configure Service Account for Gemini CLI
 print_header "Step 5: Create and Configure Service Account for Gemini CLI"