Architecting Secure Authentication and Access Control for Startups

The Importance of Early Security Architecture

Many startups defer security implementation, viewing it as a feature to be added later. However, the article strongly argues that security is a fundamental architectural layer. Retrofitting security becomes exponentially more expensive and complex as a system grows, potentially leading to significant data breach costs that can cripple a nascent company. Early architectural decisions around security are crucial for long-term stability and scalability.

Authentication & Access Control Strategies

The choice of authentication mechanism is one of the most impactful security decisions. The article outlines three primary architectural options, each with distinct trade-offs regarding development speed, flexibility, vendor lock-in, and scalability.

Option A: Full-Service Auth Platforms (e.g., Auth0, Supabase Auth)

• <strong>Pros:</strong> Fastest path to a working login system, handles MFA, session management, user dashboards, and role management with minimal code.
• <strong>Cons:</strong> Deep coupling to the platform's session and user models. Limits flexibility for separate API services, mobile apps, or custom session requirements. Migration becomes painful and expensive at scale. Per-user cost at scale can be high.

Option B: OAuth 2.0 via Frameworks (e.g., NextAuth/Auth.js)

• <strong>Pros:</strong> More flexible than full-service platforms, direct control over user records, no per-user cost. Delegates credential storage and verification to trusted OAuth providers.
• <strong>Cons:</strong> Tightly coupled to specific frontend frameworks (e.g., Next.js). Session model doesn't easily extend to a backend with multiple microservices, separate APIs (NestJS), or mobile applications without custom JWT layers. May require replacement as the system scales or diversifies.

Option C: Roll Your Own Sessions, Delegate Login to OAuth 2.0 (Recommended)

• <strong>Approach:</strong> Leverage established OAuth providers (Google, GitHub) for credential verification and MFA. Develop in-house components for JWT issuance and validation, session management (access/refresh tokens), CSRF token rotation, XSS prevention via HTTP-only cookies, and authorization logic.
• <strong>Benefits:</strong> Full control over session architecture, enabling support for mobile apps, separate APIs, and microservices from day one. Avoids vendor lock-in for session models while offloading the riskiest part of authentication (credential storage and verification) to highly secure third parties.
• <strong>Key Security Practices:</strong> Use short-lived access tokens and longer-lived refresh tokens, store refresh tokens securely for revocation, and use HTTP-only, secure, and SameSite cookies for web clients to mitigate XSS and CSRF. For mobile clients, use platform-specific secure storage (Keychain, EncryptedSharedPreferences) for bearer tokens obtained from a dedicated token endpoint.

// Example: After OAuth 2.0 callback, issue your own tokens
import { sign, verify } from "jsonwebtoken";

// Short-lived access token (15 min)
const accessToken = sign(
  { userId: user.id, role: user.role },
  process.env.JWT_SECRET ?? "",
  { expiresIn: "15m", issuer: "your-app", audience: "your-api" },
);

// Longer-lived refresh token (7 days), stored in DB for revocation
const refreshToken = sign(
  { userId: user.id, tokenVersion: user.tokenVersion },
  process.env.REFRESH_SECRET ?? "",
  { expiresIn: "7d" },
);

// Set as HTTP-only cookies (not accessible via JavaScript = XSS resistant)
res.cookie("access_token", accessToken, {
  httpOnly: true,
  secure: true,
  sameSite: "strict",
  maxAge: 15 * 60 * 1000,
});