auth layer across services

One of the hardest parts of moving to microservices isn’t breaking apart the codebase — it’s dealing with authentication and authorization.

Left unchecked, every service ends up with its own approach: JWTs here, session cookies there, half a dozen different middleware implementations. The result is duplicated logic, inconsistent user experiences, and brittle integrations.

A more sustainable pattern is to introduce a unified authentication and authorization layer, a single service responsible for identity.

One identity, many systems

In a typical distributed setup, users might come from different sources — a public user database, an internal admin portal, or third-party OAuth providers.

Instead of forcing each microservice to integrate with all of them, the auth layer normalizes these identity sources behind a single API.

For example, your system might have:

• Customers stored in a PostgreSQL-backed user service
• Partners authenticated via OAuth2 providers
• Admins managed in an internal Keycloak or Authentik instance

Rather than each microservice verifying users differently, they all delegate to a central auth service that exposes standard endpoints like /login, /introspect, and /refresh.

Microservices shouldn’t generate or verify their own JWTs.
The auth layer is the single issuer: it signs tokens, validates refresh logic, and attaches claims about roles, scopes, and tenant context.

Downstream services simply check the signature using a cached public key (JWKS) and enforce authorization rules based on claims.

To the microservices, identity becomes a verified, immutable fact — not something they need to understand deeply.

Here’s what a typical request looks like once the unified layer is in place:

# Example request to an order service
GET /orders/123
Authorization: Bearer eyJhbGciOi...

# Inside the service
verifyToken(jwt)  # validates signature using cached JWKS
enforceScopes(["orders:read"])

Integrating with my stack

This approach fits cleanly into most modern setups.

• A NestJS microservice or Express API can delegate token verification to a small middleware module.
• A GraphQL gateway (like Hasura or Apollo) can verify once at the edge and propagate the identity downstream via headers.
• Frontends interact with /login and /refresh endpoints, completely abstracted from the internals of each identity provider.

From the outside, the whole system feels like a single, well-defined identity platform — even if it’s actually orchestrating multiple backends.

Unifying authentication has its own engineering challenges:

• Every request now depends on token validation. You’ll want local caching of public keys and careful timeout handling.
• The auth service becomes critical infrastructure. It needs horizontal scaling, redundancy, and clear monitoring.
• Getting everyone to adopt it is cultural, not just technical. Teams used to “rolling their own” auth will need to buy into the common layer.

Centralizing identity pays off in the long run.

• Updating authentication flows happens once, not in 15 places.
• Authorization logic becomes consistent and auditable.
• Security incidents are easier to track and contain.

When compliance or security asks “who had access to what?”, you can answer with a single log — not a patchwork of mismatched data.

A unified authentication layer turns identity into a platform concern rather than an implementation detail.
And that’s what transforms a cluster of services into a coherent system.