firebase-auth-setup {Security} (v1.0)

"Security is not a feature. It's every feature's foundation."

Purpose

Firebase Auth: email/password, phone, anonymous, custom tokens, MFA (TOTP/SMS). Session cookies. Provider linking. [EXPLICIT] When to use: Implementing authentication, authorization, or security measures in Firebase projects.

Core Principles

1. Law of Auth First: No endpoint without authentication. Firebase ID token verification is mandatory. [EXPLICIT]
2. Law of Least Privilege: Users get minimum permissions needed. Custom claims define roles. [EXPLICIT]
3. Law of Defense in Depth: Client validation + Security Rules + Cloud Functions validation. Three layers. [EXPLICIT]

Core Process

Phase 1: Assess security requirements from spec.

Phase 2: Implement auth, authorization, and security measures.

Phase 3: Audit with OWASP checklist. Test rules with emulator.

Validation Gate

• Auth implemented on all endpoints
• Security rules cover all Firestore collections
• OWASP Top 10 mitigations addressed
• Secrets in Secret Manager (not in code)
• Privacy compliance documented

Usage

Example invocations:

• "/firebase-auth-setup" — Run the full firebase auth setup workflow
• "firebase auth setup on this project" — Apply to current context

Assumptions & Limits

• Assumes access to project artifacts (code, docs, configs) [EXPLICIT]
• Requires English-language output unless otherwise specified [EXPLICIT]
• Does not replace domain expert judgment for final decisions [EXPLICIT]

Edge Cases

Scenario	Handling
Empty or minimal input	Request clarification before proceeding
Conflicting requirements	Flag conflicts explicitly, propose resolution
Out-of-scope request	Redirect to appropriate skill or escalate