A guide for building and troubleshooting sign-in and access control on Google Cloud using Firebase Authentication, Identity Platform, Cloud Run, and service accounts.

Use it to implement or debug React sign-in flows, Firebase token handling, Cloud Run access checks, and backend access to services such as Spanner.

It helps separate the identity of an end user from the permissions used by backend services. This avoids common mistakes when sending login tokens through a frontend, proxy, and Cloud Run service.

How davenportjw/agent-skills configures Claude Code and Codex

Reuse

Borrowing it

Nothing to install: this file belongs to davenportjw/agent-skills. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/davenportjw/agent-skills/main/.skills/gcp_auth/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/davenportjw/agent-skills

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/davenportjw/agent-skills/gcp_auth/github.svg)](https://agentmods.dev/skills/davenportjw/agent-skills/gcp_auth)

Your own site

<a href="https://agentmods.dev/skills/davenportjw/agent-skills/gcp_auth"><img src="https://agentmods.dev/badge/skills/davenportjw/agent-skills/gcp_auth/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/davenportjw/agent-skills/gcp_auth"><img src="https://agentmods.dev/badge/skills/davenportjw/agent-skills/gcp_auth.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 21 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 951 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00021	$0.00951
Opus 5	$0.00010	$0.00476
Sonnet 5	$0.00004	$0.00190
Haiku 4.5	$0.00002	$0.00095

Measured 10d ago against content hash fe5dae4d53c7, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

gcp_auth scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 10d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.skills/gcp_auth/SKILL.md · 59 lines

How it starts

The opening of the file, as written. The whole thing — 59 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Google Cloud Authentication with Identity Platform and Cloud Run

User->>Frontend App (React): Log in via Firebase Auth
Frontend App (React)->>Frontend App (React): Get Firebase ID Token
Frontend App (React)->>Frontend Proxy (Express Server): API Request + Firebase ID Token (Authorization)
Frontend Proxy (Express Server)->>Frontend Proxy (Express Server): Move Firebase Token to X-Forwarded-Authorization
Frontend Proxy (Express Server)->>Frontend Proxy (Express Server): Fetch Cloud Run IAM Identity Token for Backend
Frontend Proxy (Express Server)->>Backend (Cloud Run): API Request + IAM Token (Authorization) + Firebase Token (X-Forwarded-Authorization)
Backend (Cloud Run)->>Backend (Cloud Run): Cloud Run IAM Proxy verifies IAM Token (Authorization)
Backend (Cloud Run)->>Backend (Cloud Run): API verifies Firebase Token (X-Forwarded-Authorization)
Backend (Cloud Run)->>Spanner (Database): Backend Service Account authorizes Spanner access

</context>

Read the full file on GitHub · 59 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

10d ago First seen · 59 lines · 21 tokens per session scan A fe5dae4d53c7

Subscribe to this mod's changes

gcp_auth is a skill published in the GitHub repository davenportjw/agent-skills (2 stars, last pushed 3mo ago), licensed Apache-2.0. It adds 21 tokens to every session and 951 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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agui-dotnet-protobuf

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Azure Resource Manager SDK for Bot Service in .NET. Management plane operations for creating and managing Azure Bot resources, channels (Teams, DirectLine, Slack), and connection settings. Triggers: "Bot Service", "BotResource", "Azure Bot", "DirectLine channel", "Teams channel", "bot management .NET", "create bot".

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fastapi-router-py

Create FastAPI routers with CRUD operations, authentication dependencies, and proper response models. Use when building REST API endpoints, creating new routes, implementing CRUD operations, or adding authenticated endpoints in FastAPI applications.

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aws-sdk-java-v2-core

Provides AWS SDK for Java 2.x client configuration, credential resolution, HTTP client tuning, timeout, retry, and testing patterns. Use when creating or hardening AWS service clients, wiring Spring Boot beans, debugging auth or region issues, or choosing sync vs async SDK usage.

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agent-skills: Skill for Claude Code