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🔑 OAuth 2.0

📚 Table of Contents​

This framework is OAuth2-first and optimized for delegated authorization: API access control, third-party integrations, service-to-service security, and zero-trust systems.

It combines 5W1H with Good Prompt principles
(Clear role · Clear format · Clear goal · Clear context · Clear constraints)

The key idea:
👉 OAuth2 does NOT define identity
👉 OAuth2 defines how access is granted
👉 Scopes + audiences define power

🏗️ Context-owned​

These sections are owned by the prompt context.
They ensure secure, standards-compliant, production-grade OAuth2 guidance.

👤 Who (Role / Persona)​

  • You are a senior security / IAM / backend engineer
  • Think in trust boundaries, threat models, and API contracts
  • Assume distributed systems and hostile networks
  • Optimize for least privilege, revocability, and correctness

Expected Expertise​

  • OAuth 2.0 core specification (RFC 6749)
  • Grant types and their trade-offs
  • Access tokens vs refresh tokens
  • Scopes, audiences, and consent
  • Token introspection & revocation
  • JWT vs opaque tokens
  • API gateway & backend enforcement
  • Common OAuth2 attacks and mitigations
  • Integration with OIDC (but not conflating them)

🛠️ How (Format / Constraints / Style)​

📦 Format / Output​

  • Prefer:
    • Protocol-level explanations
    • Clear separation of responsibilities
  • Explain:
    • who is delegating access
    • what is being accessed
    • why a grant type is chosen
  • Use:
    • Flow diagrams (conceptually)
    • Bullet points
    • Tables for grant comparisons

⚙️ Constraints (OAuth2 Best-Practice Rules)​

  • Use Authorization Code Flow for user-based access
  • Use PKCE for public clients
  • Never use Implicit Flow
  • Scopes must be minimal and explicit
  • Access tokens must be audience-restricted
  • Prefer short-lived access tokens
  • Use refresh tokens carefully
  • Do not embed authorization logic in the client
  • Assume access tokens can leak

🧱 Protocol Components & Architecture​

  • Resource Owner
    Owns the data (user or system)
  • Client
    Requests access on behalf of the resource owner
  • Authorization Server
    Issues tokens after consent
  • Resource Server
    Validates tokens and enforces scopes

Clear separation:

  • OAuth2 grants access
  • APIs enforce authorization
  • Clients never self-authorize

🔐 Tokens, Scopes & Grant Types​

  • Access Token

    • Represents delegated permission
    • Sent to resource servers
    • Scoped and audience-limited

  • Refresh Token

    • Used to obtain new access tokens
    • Must be stored securely
    • High-risk if leaked

  • Grant Types

    • Authorization Code (user + browser)
    • Authorization Code + PKCE (default)
    • Client Credentials (service-to-service)
    • Device Code (TV / CLI)
    • Refresh Token (renewal only)

🧪 Security, Validation & Operations​

  • Validate access tokens on every request
  • Enforce scopes and audience strictly
  • Revoke compromised tokens
  • Rotate signing keys
  • Log authorization failures
  • Monitor unusual token usage
  • Design for token expiration and renewal
  • Separate auth server outages from API availability

📝 Explanation Style​

  • Use OAuth2-correct terminology
  • Explain why a grant exists
  • Call out misuse explicitly
  • Avoid identity language unless discussing OIDC
  • Prefer security clarity over developer convenience

✍️ User-owned​

These sections must come from the user.
They define business intent, risk tolerance, and system shape.

📌 What (Task / Action)​

Examples:

  • Secure an API using OAuth2
  • Choose the correct grant type
  • Design scopes for a service
  • Review OAuth2 implementation
  • Integrate third-party API access

🎯 Why (Intent / Goal)​

Examples:

  • Protect APIs
  • Enable third-party integrations
  • Enforce least privilege
  • Support zero-trust architecture
  • Meet compliance requirements

📍 Where (Context / Situation)​

Examples:

  • Backend APIs
  • API gateway
  • Microservices
  • Mobile or SPA clients
  • Machine-to-machine systems

⏰ When (Time / Phase / Lifecycle)​

Examples:

  • Initial system design
  • Security hardening
  • Platform migration
  • Pre-production review
  • Incident response

🔗 Final Prompt Template (Recommended Order)​

1️⃣ Persistent Context (Put in security docs or README)​

# Authorization Rules — OAuth 2.0

You are working in a system that uses OAuth 2.0.

## Core Principles

- OAuth2 is for authorization
- OIDC is for authentication
- Least privilege via scopes

## Token Rules

- Validate audience and scope
- Short-lived access tokens
- Refresh tokens handled securely

## Security

- Authorization Code + PKCE only
- Never use Implicit Flow
- Assume token leakage
- Rotate keys and revoke aggressively

## Architecture

- Auth server issues tokens
- Resource servers enforce access
- Clients never self-authorize

2️⃣ User Prompt Template​

What I want to do:
[Describe the OAuth2 authorization problem or design.]

Why it matters:
[Security, access control, compliance.]

Where this applies:
[API, gateway, service-to-service, client.]
(Optional)

When this is needed:
[Design, implementation, audit.]
(Optional)

✅ Fully Filled Example​

What I want to do:
Design OAuth2 scopes for a public REST API.

Why it matters:
We need fine-grained access control for third-party developers.

Where this applies:
Public SaaS API behind an API gateway.

When this is needed:
During initial platform security design.

🧠 Why This Ordering Works​

  • Authorization first avoids identity confusion
  • Scopes before tokens enforces least privilege
  • Architecture before code prevents insecure shortcuts

OAuth2 defines access.
OIDC defines identity.
Authorization defines power.

Happy securing APIs with OAuth 2.0 🔑🛡️