Summary: SSO Has Become Essential
The moment services split into multiple parts, SSO becomes essential, not optional. For user experience and developer sanity.
Key Lessons:
- Role Separation: Identity Provider (authenticate) + Service Provider (verify)
- Choose OIDC: SAML is too heavy, OAuth isn't authentication. OIDC is the modern standard
- Use PKCE: Authorization Code Flow + PKCE is the most secure
- Three Token Types: Clearly distinguish Access (short-term), Refresh (long-term), ID (identity)
- Don't Build Your Own: Use proven services like Auth0, Clerk, Supabase
- Security Principles: httpOnly cookies, CSRF defense, Token Rotation, Session Regeneration
After building SSO, user complaints disappeared. One login grants access to all services. I escaped the hell of logging in three times. Like an amusement park wristband, one authentication opens all doors.