Designing a Scalable Authentication System for Multi-Startup SSO

As part of creating cross-company engineering standards, I was tasked with implementing authentication for eventROI. However, the goal wasn't just to build a quick login — it was to architect a shared authentication system that could support SSO across all SquadS Ventures startups. The idea: if a client uses one of our products and subscribes to another, they should be able to access it using the same account — no redundant logins, no friction.

To achieve this, I needed to:

• Design the system with future scalability and modular security in mind
• Implement proper backend guards, frontend state management, and security best practices
• Anticipate integration with multiple startups and handle transitions across different environments

Given the complexity and long-term impact of the system, I authored a detailed design document to guide both implementation and future evolution.

📄 Design Doc Highlights:

• High-level project description
• User stories with definition of done
• MVP scope (v0)
• External dependencies and cost analysis
• Data architecture and API references
• Sequence & state diagrams
• Error handling strategies and UX feedback
• Non-functional requirements (rate limiting, security, etc.)
• Rollout strategy (feature flags, progressive delivery)
• Product analytics instrumentation plan

The result is an enterprise-level SSO infrastructure, built to support future migrations (e.g. between auth providers) with minimal friction. It's now the foundation for account management across all upcoming SquadS products.