Tell us about a complex authorization task when transitioning from monolith to microservices.

When transitioning from a monolith to microservices, authentication becomes significantly more complex due to the distributed nature of the system. Main challenges and approaches:

• Centralized management of authentication and authorization. In a monolith, there is usually a single entry point where the user and their rights are verified. In microservices, a unified mechanism must be provided, for example, through OAuth 2.0 / OpenID Connect, where a dedicated authentication service issues tokens (JWT).

• Passing user context between services. Each microservice must receive and validate the user's token to make authorization decisions. This requires standardization of token formats and validation mechanisms.

• Distributed authorization. In some cases, microservices need to make access decisions based on roles or rights, which can be stored centrally or locally. This may require implementing authorization services (e.g., using Policy Decision Point - PDP).

• Ensuring security and minimizing trust. Each service should independently verify access rights to avoid vulnerabilities.

• Handling rights updates and token revocation. In a monolith, updating user rights is simpler; in microservices, mechanisms for token invalidation or rights updates without re-authentication need to be considered.

• Example solutions:

  • Using an API Gateway that verifies tokens and passes user information in headers.
  • Microservices validate tokens locally (e.g., verify JWT signatures).
  • For complex authorization rules, a dedicated authorization service is used, which microservices call when needed.

Thus, transitioning requires implementing authentication and authorization standards, as well as a well-thought-out architecture for service interaction to ensure security and convenience.