5 min read
User Authentication
Some apps need to know who’s using them. This guide covers when you need authentication and the simplest approaches to implement it.
When You Need Auth
You need auth when:
- Users have personal data (their notes, their settings)
- Content should be private
- You need to identify who did what
- Features differ by user
You don’t need auth when:
- Tool is stateless (input → output)
- All users see the same content
- No personal data is stored
- It’s a simple utility
Ask yourself:
“Does this app need to remember anything about specific users?”
If no, skip auth. It adds complexity.
Simple Approaches
Magic links (easiest)
User enters email, receives a login link, clicks to authenticate.
Add magic link authentication.
User enters email, receives a link, clicking the link logs them in.Pros:
- No passwords to manage
- Familiar to users
- Hard to get wrong
Cons:
- Requires email service
- Slight friction (check email)
OAuth (social login)
“Sign in with Google/Apple/GitHub”
Add Sign in with Google authentication.Pros:
- Users don’t create new passwords
- Trusted providers handle security
- Quick to implement with libraries
Cons:
- Dependent on external providers
- Some users prefer not to link accounts
Password-based
Traditional username/password.
Add email and password authentication.
Include password reset functionality.Pros:
- Users understand it
- No external dependencies
Cons:
- Must handle password security properly
- Password reset is complex
- Users forget passwords
Auth Services
These handle the hard parts for you:
Clerk
- Drop-in components
- Handles everything
- Good free tier
Auth0
- Enterprise-ready
- Extensive features
- More complex setup
Supabase Auth
- Part of Supabase platform
- PostgreSQL integration
- Good for full-stack apps
Firebase Auth
- Google’s solution
- Multiple providers
- Good documentation
Prompting for auth setup
Add authentication using [Clerk/Auth0/Supabase].
Set up sign up, sign in, and sign out.
Protect [these routes/features] for logged-in users only.What Auth Gives You
User identity
- Know who’s logged in
- Associate data with users
- Personalize experience
Protected routes
- Some pages require login
- Redirect unauthorized users
- Show/hide features based on auth state
Session management
- Remember logged-in users
- Handle logout
- Token refresh
Implementation Patterns
Auth state in UI
Show the user's name in the header when logged in.
Show "Sign in" button when logged out.Protected pages
Redirect to login if user tries to access [page] without being logged in.
After login, redirect back to the page they wanted.Auth-dependent features
Only show the "Save" button if the user is logged in.
If not logged in, show a prompt to sign in.Storing User Data
Profile information
Store the user's profile (name, avatar, preferences)
in [database/Supabase/Firebase].
Load it when they log in.User-specific content
Each user should only see their own [notes/projects/items].
Filter the data by the logged-in user's ID.Settings
Save user preferences (theme, notification settings)
associated with their account.Privacy Considerations
Collect only what you need
- Don’t ask for data you won’t use
- Email is often enough to start
Be transparent
- Tell users what you collect
- Provide a privacy policy
- Allow data export/deletion
Handle data carefully
- Use HTTPS everywhere
- Don’t log sensitive data
- Consider data retention
Prompting for privacy
Make sure authentication follows privacy best practices.
Don't store unnecessary data.
Use secure connections.Common Auth Flows
Sign up
- User enters email (+ password or magic link)
- Verify email
- Create account
- Log them in
Sign in
- User enters credentials
- Verify credentials
- Create session
- Redirect to app
Sign out
- User clicks logout
- Destroy session
- Redirect to home/login
Password reset
- User requests reset
- Send email with reset link
- User clicks link
- User sets new password
Debugging Auth Issues
User can’t log in
Users are getting stuck at login.
[Describe what happens]
Error: [paste if available]Session not persisting
Users keep getting logged out.
The session isn't being saved properly.OAuth errors
Sign in with [provider] is failing.
Error: [paste error]
Here's my OAuth configuration: [describe]What You’ll Learn
- When authentication is necessary
- Different auth approaches and trade-offs
- Using auth services
- Protecting routes and features
- Storing user-specific data
- Privacy considerations