Project 15: OAuth Lifecycle and Identity Propagation Hardening

Implement secure, resilient OAuth behavior with deterministic recovery, scope enforcement, and tenant-safe identity mapping.

Quick Reference

Attribute Value
Difficulty Advanced
Time Estimate 2 weeks
Main Programming Language TypeScript
Alternative Programming Languages Python, Go
Coolness Level Level 4
Business Potential Essential for integrations
Prerequisites OAuth basics, API authz understanding
Key Topics PKCE, token lifecycle, mcp/www_authenticate, identity propagation

1. Learning Objectives

  1. Implement tool-level scope declarations and enforcement.
  2. Handle auth challenges using structured metadata.
  3. Build safe refresh/revocation lifecycle handling.
  4. Propagate identity into backend domain context securely.

2. All Theory Needed (Per-Concept Breakdown)

Secure Authorization for Conversational Tools

Fundamentals OAuth success is not login success. Your app must continuously enforce scopes and identity context at execution time.

Deep Dive into the concept Define security schemes per tool and avoid over-broad shared scopes. When token context is missing or invalid, return a structured challenge through mcp/www_authenticate so clients can trigger clean re-auth.

Use authorization code with PKCE for public-facing flows. Keep access tokens short-lived and rotate refresh tokens. Store credentials server-side only, encrypted at rest, and never pass bearer tokens to widget state or logs.

Identity propagation is a separate concern from token storage. Convert token claims into internal user/tenant IDs and pass only that minimal context to tool handlers. Re-validate tenant mapping per write action.

Test lifecycle edges aggressively: expired access token, revoked refresh token, insufficient scope, and stale tenant association. These failures should be deterministic and recoverable.

Minimal concrete example

auth_error:
  code=AUTH_REQUIRED
  _meta["mcp/www_authenticate"]='Bearer realm="crm", error="invalid_token"'
  retryable=true

3. Project Specification

3.1 What You Will Build

A hardened OAuth subsystem integrated with tool security schemes, challenge responses, rotation policies, and identity-safe backend calls.

3.2 Functional Requirements

  1. Declare per-tool auth scopes.
  2. Emit structured auth challenges.
  3. Implement refresh rotation and revocation handling.
  4. Enforce tenant-safe identity propagation.

3.3 Real World Outcome

$ npm run auth:lifecycle-test
[ok] challenge via mcp/www_authenticate
[ok] code+pkce exchange
[ok] scope validation at tool execution
[ok] refresh rotation
[ok] revoked token path
[ok] tenant-safe identity propagation
critical_auth_failures=0

4. Solution Architecture

Tool Security Scheme -> OAuth Challenge -> Token Exchange -> Scope + Tenant Validation -> Backend Action

5. Implementation Guide

5.1 The Core Question You’re Answering

“Can the app preserve least-privilege security without breaking user workflows when credentials change?”

5.2 Concepts You Must Understand First

  1. OAuth 2.0 + PKCE flow.
  2. Scope matrix and authorization boundaries.
  3. Tenant identity mapping and validation.

5.3 Questions to Guide Your Design

  1. Which scopes are minimal per tool?
  2. How are auth errors classified and recovered?
  3. Where is identity context derived and verified?

5.4 Thinking Exercise

Map the full sequence for expired token during mutating operation and define each security check.

5.5 The Interview Questions They’ll Ask

  1. Why emit structured auth challenges?
  2. How do you enforce least privilege per tool?
  3. How do you design safe refresh-token handling?
  4. How do you avoid cross-tenant writes?
  5. How do you monitor auth health in production?

5.6 Hints in Layers

  • Hint 1: Build a per-tool scope matrix first.
  • Hint 2: Normalize auth error classes.
  • Hint 3: Keep token handling server-side only.
  • Hint 4: Add lifecycle chaos tests before release.

5.7 Books That Will Help

Topic Book Chapter
OAuth deep dive “OAuth 2 in Action” Core protocol chapters
Identity boundaries “Domain-Driven Design” Identity sections
Security controls “Foundations of Information Security” Access control chapters

6. Testing Strategy

  • Full OAuth lifecycle tests.
  • Insufficient-scope and revoked-token tests.
  • Multi-tenant identity boundary tests.

7. Common Pitfalls & Debugging

Pitfall Symptom Solution
Shared over-broad scopes Excess privilege Define narrow per-tool scopes
Refresh token failures Random auth drops Add rotation and replay-safe handling
Tenant mismatch Wrong data mutations Validate tenant context on each write

8. Extensions & Challenges

  • Add external identity provider portability tests.
  • Add automatic scope-upgrade UX flow.
  • Add auth anomaly alerting runbook.

9. Real-World Connections

  • Enterprise SaaS integrations
  • Security-critical API connector platforms
  • Multi-tenant authorization systems

10. Resources

  • OpenAI Apps SDK: Authenticate users
  • RFC 6749, RFC 7636, RFC 9728
  • Model Context Protocol authorization docs

11. Self-Assessment Checklist

  • I can design per-tool scope boundaries.
  • I can implement deterministic auth challenge/recovery behavior.
  • I can prove tenant-safe identity propagation.

12. Submission / Completion Criteria

Minimum Viable Completion

  • Working challenge/reconnect flow with scope validation.

Full Completion

  • Full lifecycle hardening, tenant boundary tests, and auth observability metrics.