Introduction
In today’s digital landscape, security is no longer optional—it’s essential. At the heart of security lies authentication, the first gatekeeper to your app or service.
Choosing the right authentication method isn’t just about security—it’s about user experience, scalability, and future-proofing your system. Whether you’re building a mobile app, a web dashboard, or a B2B SaaS platform, picking the wrong auth flow can cost you users—or worse, leave you vulnerable to attacks.
In this guide, we’ll explore popular backend authentication methods—OAuth, OTP, and Magic Links—and help you decide which one (or combination) fits your app best.
What Is Authentication?
Before diving in, let’s clarify a common confusion:
- Authentication: Proving who you are.
- Authorization: Deciding what you're allowed to do.
They go hand in hand—but in this blog, we focus on authentication.
There are two major schools of thought:
- Password-based authentication: The classic “email + password” combo.
- Passwordless authentication: Logging in without a password—via a code, link, or third-party identity provider.
With data breaches on the rise and users overwhelmed by passwords, passwordless is gaining traction fast.
OAuth (Open Authorization)
What is OAuth?
OAuth is a protocol that lets users log in using another service (like Google, Facebook, GitHub), without giving your app their password. It also allows apps to access user data (like profile info or contacts) from other platforms securely.
How OAuth Works (Simplified Flow)
- User clicks “Login with Google”
- Redirects to Google login page
- User logs in and consents to data sharing
- Google sends your app a secure token
- Your backend verifies the token and grants access
There are two common OAuth flows:
- Authorization Code Flow – for web apps
- PKCE (Proof Key for Code Exchange) – for mobile apps and SPAs
Pros:
- High security (tokens, scopes, expirations)
- No password handling needed
- Users trust familiar platforms
Cons:
- Complex to implement and debug
- Relies on third-party services (if Google is down, login fails)
When to Use:
- Apps that support social login
- Microservices or API systems
- Third-party integrations (e.g., pulling data from Google APIs)
OTP (One-Time Password)
What is OTP?
OTP is a time-sensitive, single-use code sent to the user—usually via SMS, email, or an authenticator app—used to verify identity.
Types of OTP:
- SMS OTP
- Email OTP
- Call OTP
- Authenticator apps (e.g., Google Authenticator, Authy)
Pros:
- Familiar to users
- Works well for MFA (multi-factor authentication)
- Doesn’t require remembering passwords
Cons:
- Susceptible to SIM-swapping, phishing, and email interception
- Can cause friction (users waiting for the code)
- Relies on third-party delivery systems
When to Use:
- 2FA (in addition to passwords or OAuth)
- Passwordless login
- Time-limited verifications, like during sign-up or sensitive actions
Magic Links (Verification Links)
What is a Magic Link?
A magic link is a one-time-use, time-sensitive URL sent to the user’s email. Clicking it logs them in—no password, no code.
How It Works:
- User enters email
- App sends a login link with a token
- User clicks the link → Authenticated!
Pros:
- Extremely simple for users
- Great for onboarding and re-engagement
- Secure if implemented properly (short lifespan, single-use tokens)
Cons:
- Email delivery delays can hurt UX
- Risky if links are reused or not time-bound
- Phishing risks if users aren’t trained
When to Use:
- Low-risk applications
- One-click login flows
- Onboarding or email verification
Security Comparison
| Method | Security Level ⭐ | Ease of Use 😊 | Best Use Case |
|---|---|---|---|
| OAuth | ⭐⭐⭐⭐☆ | Medium | Social login, third-party APIs |
| OTP | ⭐⭐⭐☆☆ | High | 2FA, passwordless, sensitive actions |
| Magic Link | ⭐⭐☆☆☆ | Very High | Onboarding, quick sign-ins |
Other security considerations:
- Token expiration (short-lived = safer)
- Replay attacks (OTP/Magic Links should be single-use)
- MITM risks (use HTTPS, validate tokens)
- Rate-limiting to avoid brute-force attempts
Choosing the Right One
Ask yourself:
- Is this a web, mobile, or API-based app?
- Are you B2C (mass users) or B2B (fewer, high-value users)?
- How sensitive is the data involved?
- What is your user’s tolerance for login friction?
- Do you need third-party integrations?
| App Type | Suggested Auth |
|---|---|
| Consumer Mobile | OAuth (social) + OTP (MFA) |
| Admin Dashboard | Magic Link + OTP |
| SaaS B2B | Email/password + OAuth (Google Workspace) |
| Public API | OAuth (client credentials or token flow) |
Combining Methods
No rule says you must choose just one.
Real-world examples:
- Google uses OAuth for login, but asks for OTP on suspicious activity
- Slack allows login via magic link, but also supports Google OAuth
- Banking apps often use passwords + OTP + device binding
Combining methods lets you balance security with user convenience.
Conclusion
There’s no universal “best” authentication method. The right one depends on:
- Your application’s risk profile
- User expectations
- Technical constraints
- Regulatory requirements
Authentication is the front door to your app—make sure it's not a revolving door or a brick wall.
When in doubt, start simple, follow best practices (like OWASP’s guidelines), and iterate based on real user behavior and security audits.
Bonus: Developer Resources
- OWASP Authentication Cheat Sheet
- OAuth 2.0 Flows Explained
-
Example Code:
Tips:
- Use diagrams to illustrate auth flows (OAuth steps, OTP loop, Magic Link lifecycle).
- Add code snippets for real implementation.
- Include links to libraries or tools (e.g., Firebase Auth, Auth0, Passport.js).
Top comments (1)
We went down the route of not supporting magic links altogether. I think it's a hill that we'll die on and one that enough customers asked about that I had to write an official blog post about it since we kept responding with the same pre-written statement in the support chats.
OAuth has taken over most of the auth flows though, especially with almost everyone using the "Sign in with Google" or related social network path. It's easy and you're relatively confident that they'll have an account with one of the big social or mail providers.