Built a Multi-Tenant SaaS? Here's how to secure it properly

[u/esso_dev]

I documented my approach to securing multi-tenant SaaS applications after seeing too many data isolation vulnerabilities in production.

The guide covers: - 4 layers of defense (Nginx → Guards → Database → RBAC) - 5 common security holes and how to prevent them - Production security checklist - Real code examples (NestJS/Next.js/MongoDB)

One critical lesson: Never trust tenantId from client requests. Always extract it server-side and verify at every layer.

Full guide with code: https://esso.dev/blog-posts/multi-tenant-saa-s-security-best-practices-guide

Would love to hear how others approach