How should I implement paid tier permissions using Stripe in a Spring Boot microservices architecture?

Below is a recommended approach using Stripe for managing paid tiers, considering both security and efficiency:

Centralizing Tier Checking at the Gateway

• Single Point of Validation:
  Implementing tier and permission checking in your API gateway allows you to validate that a user is eligible for a given action before forwarding the request to the downstream microservice. This central check can reduce unnecessary network calls between multiple microservices.

• Performance Benefits:
  Performing the check at the gateway can cut down on the overhead of each microservice having to call the subscription service, leading to faster request handling. You could further optimize this by embedding subscription details into tokens (with secure, short-lived caches) so the gateway can quickly validate permissions without an extra round-trip.

• Ease of Maintenance:
  Having a single authorization layer simplifies updating policies or integrating changes (for example, if Stripe subscription details change). It keeps your business logic in each microservice free from additional subscription logic, making your system easier to maintain.

When to Consider Additional Checks in Microservices

• Sensitive or Critical Actions:
  If some operations are highly sensitive or require re-validation in case of long-lived sessions, you might also have microservices perform an extra check with the subscription service. This can act as a safety net, ensuring data consistency and handling edge cases where a user's subscription might have changed between requests.

• Service-to-Service Trust:
  Typically, if the gateway has done thorough authentication and authorization, downstream microservices can trust that the request is valid. However, in scenarios involving critical actions, an additional verification in the microservice may be warranted.

Recommended Strategy

1. Primary Check at the Gateway:

   • Have the API gateway validate the user’s subscription tier using the subscription microservice or cached credentials.
   • Reject requests early if the user’s tier does not permit the requested operation.

2. Optional Secondary Check in Microservices:

   • For operations that are particularly sensitive, perform an extra check within the microservice itself before processing the request. This can help ensure that no changes in subscription status or tier have occurred since the gateway’s check.

By centralizing the permission logic at the gateway level, you reduce redundant calls, improve performance, and simplify your overall system architecture. At the same time, having provisions for secondary checks when needed can bolster security for critical operations.

This balanced method leverages both efficiency and security while utilizing Stripe’s subscription features to implement tiered access control in your app.