How to Build a Secure Login System: Passwords, MFA, Sessions, and Account Recovery
A login system is more than a password check. It includes credential storage, brute-force resistance, MFA/passkeys, session creation, recovery, and security-event handling.
Store Passwords With Password Hashing
Never store plaintext or reversibly encrypted passwords. Use a dedicated slow password-hashing function.
OWASP currently recommends Argon2id when available, with scrypt as a fallback and PBKDF2 for environments with specific FIPS requirements. Tune cost parameters for your production hardware and plan to upgrade them over time.
Do Not Weaken Passwords With Arbitrary Composition Rules
Allow long passwords/passphrases and block known-compromised/common passwords where practical. Avoid silently truncating user passwords.
Resist Credential Stuffing
Rate-limit authentication and recovery by multiple signals such as account, IP/network, device/risk context, and tenant where relevant.
Avoid permanent account lockouts that attackers can weaponize for denial of service. Escalate friction progressively and monitor unusual failures.
Add Strong MFA or Passkeys
MFA materially reduces damage from stolen passwords. Phishing-resistant methods such as passkeys/security keys are stronger than SMS or one-time codes for high-value accounts.
Protect MFA enrollment and recovery as carefully as login itself; an attacker who can reset MFA owns the account.
Create a Secure Session
After authentication, issue a fresh unpredictable session/token, rotate identifiers at privilege changes/login, set appropriate expiry, and use secure cookie attributes for browser sessions.
Logging out or changing credentials should invalidate the relevant server-side session/refresh state according to the product's security model.
Secure Account Recovery
Forgot-password responses should not reveal whether an email/account exists. Recovery tokens should be:
- cryptographically random
- short-lived
- single-use
- stored safely
- invalidated after use
Do not automatically modify or lock the account until a valid recovery proof is presented.
Monitor Security Events
Record events such as successful/failed logins, password changes, MFA changes, recovery, suspicious session creation, and administrative account actions without logging credentials.
Final Takeaway
A secure login architecture protects the whole account lifecycle, not just password verification: strong password hashing, abuse controls, MFA/passkeys, secure sessions, hardened recovery, and useful security telemetry all work together.
References
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