Complete Guide to Building Secure Authentication (Part 2)

Dec 24

Authentication & Login Security Checklist

Use this checklist when building any app with user login to ensure you don't miss critical security features.

In Part 1, you learned WHY authentication security matters and HOW each feature works. In my Replit Authentication Prompt post, you got the complete copy-paste prompt to build it.

Now comes Part 2: The Checklists.

Think of this as your quality assurance toolkit. Before you deploy, before you launch, before you tell anyone your app is ready, run through these checklists. They're compiled from 15+ years of building secure systems and represent the security features that separate hobby projects from production-ready applications.

This is Part 2 of a multi-part checklist series. I'm breaking this into digestible pieces so you can focus on one area at a time without getting overwhelmed.

In This Post (Part 2 - Core Security):

Basic Requirements (registration, login, passwords)
Error Messages (critical for security AND UX)
Security Features (validation, rate limiting, data protection)
Customer Experience
Admin Security
Background Jobs
Logging & Monitoring
Common Mistakes to Avoid

Coming in Future Parts:

Part 3: Testing & Deployment Checklist

Part 4: Advanced Security & Compliance

Part 5: Performance & Scaling Checklist

How to Use This Checklist:

Print it or keep it open in another tab
Check off items as you build/verify
Don't skip items, they're all here for a reason

Come back to this for every new project

Already built your authentication system? Use this to audit what you have and identify gaps.

Haven't built it yet? Start with my Replit prompt, then use this to verify everything works.

Let's make sure your app is secure before it goes live.

BASIC REQUIREMENTS (Must Have - No Exceptions!)

Registration & Signup

Email and password are required fields
First name and last name are collected
Password must be at least 12 characters long
Password must include uppercase, lowercase, numbers, and special characters
Show a real-time password strength indicator (weak/medium/strong)
Show password requirements BEFORE user starts typing
Send verification email that expires in 24 hours
Users cannot login until they verify their email
Delete unverified accounts after 48 hours automatically

Login System

Login uses email and password only (no username)
Password field is hidden by default with show/hide toggle button
Lock account after 20 failed login attempts
Send email notification when account is locked
Account stays locked for 24 hours OR until admin unlocks it
Show clear message: "Your account has been locked for security. Try again in 24 hours."

Password Reset

"Forgot Password" link on login page
Reset email expires in 24 hours
After 8 reset attempts, delay email by 5 minutes
New password must meet the same complexity requirements
Send confirmation email after successful password change

Password Security

NEVER store passwords in plain text
Use bcrypt or Argon2 to hash passwords
Prevent users from reusing their last 5 passwords
All password fields hide text by default (show dots/asterisks)

Session Management

Auto-logout after 30 minutes of inactivity (customers)
Auto-logout after 15 minutes of inactivity (admins)
Use secure cookies (httpOnly and secure flags)
Destroy session completely on logout

ERROR MESSAGES (Critical for Security!)

What Users Should See:

✅ "The email or password is incorrect. Please try again."
✅ "This email is already registered. Please try logging in."
✅ "Your password must include at least one uppercase letter."
✅ "We're experiencing technical difficulties. Please try again shortly."

What Users Should NEVER See:

❌ "Error 4042: Database constraint violation"
❌ "Authentication failed (ERR_AUTH_001)"
❌ "Password hash comparison failed"
❌ "500 Internal Server Error"
❌ Any error codes, system codes, or technical jargon

RULE: If an error message mentions code, database, system, or technical terms - FIX IT IMMEDIATELY!

SECURITY FEATURES (Must Have)

Input Validation

Validate and sanitize ALL user inputs
Prevent SQL injection attacks
Prevent XSS (Cross-Site Scripting) attacks
Reject emails that don't match proper email format
Reject passwords that don't meet complexity requirements

Rate Limiting

Limit login attempts (lock after 20 failures)
Limit password reset requests (delay after 8 attempts)
Limit API calls per user to prevent abuse
Add delays between failed attempts (exponential backoff)

Email Verification

Email verification links expire in 24 hours
Each verification link can only be used once
Send new verification email if requested
Clear message when link expires

Data Protection

Use HTTPS/TLS 1.2+ for ALL connections
Never send passwords in URLs or query parameters
Don't reveal if an email exists in the system (same error message)
Store sensitive data encrypted in the database

CUSTOMER EXPERIENCE (Keep It Simple!)

Customer Profile Page

View and edit first name and last name
View email (but can't edit without verification)
Change password with current password required
View recent login activity (date/time only)
Logout button
Delete account option (with confirmation)

What Customers Should NOT See:

❌ Admin features or settings
❌ Other users' information
❌ System logs or technical details
❌ Database errors or codes

ADMIN SECURITY (Extra Protection!)

Admin Account Setup

Admins MUST use Multi-Factor Authentication (MFA)
Admin MFA via 6-digit email code
Admin accounts cannot be created through public signup
First Super Admin created during initial setup
dmin sessions timeout after 15 minutes (shorter than customers)

Admin Access Controls

Require password re-entry for sensitive actions:
Unlocking customer accounts
Deactivating accounts
Viewing detailed logs
Send email alert to all Super Admins when any admin logs in
Log every admin action with timestamp and IP address

Admin Dashboard Features

View all customers (name, email, status, last login)
Search and filter customers
Unlock locked accounts (with justification note)
Force logout customer sessions
Deactivate/reactivate accounts
View customer login history
View system overview (total users, active sessions, failed logins)

What Admins Can/Should NOT Do:

❌ Reset customer passwords directly
❌ See customer passwords (not even admins!)
❌ Login as a customer
❌ Bypass MFA

EMAIL TEMPLATES NEEDED

Make sure your app sends these emails:

Customer Emails:

Email verification (with link that expires in 24 hours)
Welcome email after verification
Password reset link (expires in 24 hours)
Account locked notification
Account unlocked by admin notification
Password changed confirmation
Account deleted confirmation

Admin Emails:

Admin MFA code (6 digits, expires in 10 minutes)
Admin login alert (to all Super Admins)
Failed admin login attempts (after 5 failures)
Background job failures
Suspicious activity alerts

BACKGROUND JOBS (Automated Maintenance)

Set up these automatic tasks:

Delete unverified accounts after 48 hours
Clean up expired password reset tokens
Clean up expired email verification tokens
Clean up expired MFA codes
Archive old logs (based on retention policy)
Optional: Auto-unlock accounts after 24 hours
Monitor email delivery failures

Background Job Monitoring:

By default, all background jobs added by the Replit agent works behind the scenes unattended, but in a production enviroment, you need to know their status, ideally from your app's dashboard.

Display job status in admin dashboard
Show last run time and status (success/failure)
Alert admins when jobs fail
Allow manual trigger (admins only)

LOGGING & MONITORING (Know What's Happening)

What to Log (Admin View Only):

All login attempts (successful and failed)
Account lockouts and unlocks
Password reset requests
Password changes
Admin actions (who did what, when)
Failed MFA attempts
Email delivery failures
Background job results

What NOT to Log:

❌ Actual passwords (never ever!)
❌ Full credit card numbers
❌ Social security numbers
❌ Other sensitive personal data

COMMON MISTAKES TO AVOID

Security Mistakes:

❌ Storing passwords in plain text → ✅ Always hash with bcrypt/Argon2
❌ Using weak password requirements → ✅ Enforce 12+ chars with complexity
❌ Not limiting login attempts → ✅ Lock after 20 failures
❌ Sending passwords in emails → ✅ Only send reset links, never passwords
❌ Not using HTTPS → ✅ Always use HTTPS/TLS
❌ Exposing technical errors to users → ✅ Show friendly messages
❌ Not validating user input → ✅ Validate and sanitize everything
❌ Allowing admins to reset customer passwords → ✅ Only unlock, customers reset themselves

User Experience Mistakes:

❌ Showing error codes to users → ✅ Use plain language
❌ Not explaining why password was rejected → ✅ Show specific requirements
❌ Making forms too complicated → ✅ Keep it simple (name, email, password)
❌ Not confirming actions → ✅ Send confirmation emails
❌ Confusing navigation → ✅ Clear buttons and labels

Admin Mistakes:

❌ Not protecting admin accounts → ✅ Require MFA for all admins
❌ Not logging admin actions → ✅ Log everything admins do
❌ Allowing admins to see passwords → ✅ Nobody sees passwords, ever
❌ Not requiring password re-entry → ✅ Sensitive actions need password

Wrapping Up

I hope you find this first checklist compilation helpful in building secure, production-ready applications. Whether you're launching your first SaaS platform, building an e-commerce site, or creating any customer-facing web app, this checklist gives you the security foundation you need without requiring deep security expertise.

Found a Gap?

Don't panic. Go back to the Replit prompt, add the missing feature, test it, and check it off. That's the beauty of checklists, they show you exactly where you are and what's left to do.

Remember: security doesn't have to be complicated, it just has to be done right from the start.

Now go build something secure.

Saif Khan