Do I need a separate identity service for my API?

Not always.

Whether you need a separate identity service depends on how your API is used, how many clients you have, and how much auth complexity you want to manage yourself.

You probably do not need a separate identity service if:

• Your API is small or internal
• You only have one frontend or a few trusted clients
• Basic login/session handling is enough
• You can use a managed provider like Auth0, Clerk, Cognito, Firebase Auth, Entra ID, etc.
• You’re okay with your main app also handling authentication logic

In that case, your API can simply:

• verify JWTs/access tokens
• trust a single external identity provider
• enforce roles/permissions locally

You might want a separate identity service if:

• You have multiple apps/services that need shared authentication
• You need SSO across products
• You support many client types: web, mobile, partner APIs, internal services
• You need centralized user management, MFA, password resets, account linking, auditing
• You want to separate concerns for security, scaling, or compliance
• You’re building a platform where auth is a core capability

A separate identity service usually handles:

• authentication
• token issuance
• session management
• user registration/login
• MFA
• password recovery
• federation with external IdPs
• client/app management

Your API then becomes a resource server that validates tokens and authorizes requests.

Rule of thumb

• If auth is not your product, don’t build your own identity service first.
• Start with a managed identity provider.
• Build a custom identity service only if you have a strong business or architectural reason.

Common architecture

• Identity provider issues tokens
• API validates tokens and checks authorization
• Frontend/mobile app redirects users to login or uses OAuth/OIDC
• Optional gateway enforces coarse-grained auth at the edge

When people regret not separating identity

They often start with auth inside the API, then later need:

• multiple apps
• service-to-service auth
• enterprise SSO
• tenant isolation
• security audits

At that point, splitting identity out can be painful.

Practical recommendation

If you’re unsure:

1. Use a managed identity provider
2. Keep auth logic out of your business API as much as possible
3. Design your API to accept and validate standards-based tokens (OAuth2/OIDC/JWT)
4. Only create a separate identity service if/when requirements justify it

If you want, I can also help you decide based on your specific setup, e.g.:

• internal API vs public API
• monolith vs microservices
• web/mobile/third-party clients
• current auth approach