Security is not an afterthought—it must be architected from day one. Understand the mechanics of modern web vulnerabilities, token encryption, and zero-trust authentication.
A random session ID is stored in an HTTP-only cookie. The server stores session data in Redis or database. Revocation is instantaneous, but requires database lookups on every request.
Cryptographically signed tokens containing user claims. Verified via public key or HMAC without database I/O. Ideal for distributed microservices, but difficult to invalidate before expiration.
Step-by-step breakdown of common attacks and concrete defensive code strategies.
Untrusted user input is directly concatenated into dynamic query strings, allowing attackers to execute arbitrary database commands.
Always use parameterized queries, prepared statements, or strongly typed ORMs (Prisma, SQLAlchemy). Never concatenate strings into SQL.
Malicious JavaScript injected into pages viewed by other users, stealing session cookies, auth tokens, or rewriting the DOM.
Use frameworks that auto-escape (React JSX). Set Content-Security-Policy (CSP) headers and store auth tokens in HTTP-only cookies.
An attacker tricks a victim's authenticated browser into sending unauthorized requests (e.g. money transfer or password change) to a target site.
Enforce SameSite=Lax or Strict on session cookies and validate anti-CSRF synchronizer tokens on state-changing requests.
Weak password hashing (MD5/SHA1), missing multi-factor authentication, or session fixation allowing account takeovers.
Hash passwords with Argon2id or bcrypt (cost >= 12). Enforce MFA, implement rate limiting on login attempts, and use established protocols (OAuth 2.0 PKCE).
Setting `Access-Control-Allow-Origin: *` while passing `Allow-Credentials: true`, allowing malicious third-party origins to read private user responses.
Explicitly whitelist exact trusted domains. Never reflect arbitrary Origin request headers in access control responses.