The Complete Guide to SaaS Authentication

What is SaaS Authentication?

Authentication answers the question: "Who is this user?"

For SaaS applications, auth is foundational. Every feature depends on knowing who's accessing it. But auth for SaaS has unique requirements:

Authentication Methods

Passwords (Traditional)

Users create and remember passwords.

Pros:

Cons:

Magic Links (Passwordless)

Email a login link that authenticates the user.

Pros:

Cons:

Magic links are increasingly popular for SaaS. Companies like Slack, Notion, and Medium use them.

Social Login (OAuth)

Let users sign in with Google, GitHub, etc.

Pros:

Cons:

Enterprise SSO (SAML, OIDC)

Integration with company identity providers (Okta, Azure AD).

Pros:

Cons:

Passkeys (WebAuthn)

Biometric or hardware key authentication.

Pros:

Cons:

Auth for Different SaaS Types

B2C SaaS

Individual users signing up for themselves.

Recommended approach:

B2B SaaS (SMB)

Small-medium businesses, often one person signing up initially.

Recommended approach:

B2B SaaS (Enterprise)

Large organizations with IT departments.

Recommended approach:

The Auth + Billing Connection

For SaaS, authentication and billing are deeply connected:

If auth and billing are separate systems, you must keep them in sync:

This is fragile. StackBE solves it by unifying auth and billing—one customer identity with subscription status attached.

Learn more: StackBE vs Auth0 and StackBE vs Clerk

Session Management

After authentication, you need sessions:

JWT Tokens

Stateless tokens containing user identity.

Pros:

Cons:

Session Cookies

Server stores session, client holds ID.

Pros:

Cons:

For most SaaS apps, short-lived JWTs with refresh tokens offer good balance.

Security Best Practices

Always Use HTTPS

No exceptions. Auth without HTTPS is broken.

Implement Rate Limiting

Prevent brute force attacks:

Secure Password Storage

If using passwords:

Handle Sessions Properly

Validate Email Addresses

For magic links especially:

Build vs Buy

Building Auth In-House

Pros:

Cons:

Using an Auth Provider

Pros:

Cons:

For most teams, buying auth makes sense. The risk of getting security wrong is high.

Choosing an Auth Provider

Questions to Ask

1. What auth methods do you need? Magic links only? Social? SSO?

2. Do you need billing integration? Most auth providers don't include it.

3. What's the pricing model? Per user, per MAU, flat fee?

4. How's the developer experience? SDKs, docs, support?

5. What about B2B features? Organizations, team management?

Provider Options

See our detailed comparisons:

Getting Started

If you're building a SaaS and need auth:

1. Choose auth methods - Magic links are a good default for most SaaS

2. Decide on billing integration - Separate or unified?

3. Select a provider - StackBE for unified, Clerk/Auth0 for auth-only

4. Implement login flow - Use provider SDKs

5. Handle sessions - JWTs with refresh tokens

6. Add organization support - If B2B

StackBE provides magic link auth connected to billing and entitlements—one system for identity and access.