Change the way STS agent is authenticated.

sts-agent/compose.yaml

@@ -8,9 +8,9 @@ services:
       - /etc/sts-agent:/transfer_root/etc/sts-agent:ro
       - /var/lib/vault-cert/wif:/transfer_root/var/lib/vault-cert/wif:ro
     environment:
+      GOOGLE_APPLICATION_CREDENTIALS: /transfer_root/etc/sts-agent/cred.json
       GOOGLE_API_CERTIFICATE_CONFIG: /transfer_root/etc/sts-agent/certificate_config.json
     command:
       - --project-id=${PROJECT_ID}
-      - --creds-file=/transfer_root/etc/sts-agent/cred.json
       - --hostname=${HOSTNAME}
       - --agent-pool=${STS_AGENT_POOL}