Understanding Authorization vs Authentication

The distinction between authentication and authorization is fundamental to API security, yet these concepts are often confused. Authentication answers "Who are you?" while authorization answers "What can you do?" A properly authenticated user might still be unauthorized to access certain resources or perform specific actions. This separation of concerns enables flexible security policies that adapt to complex business requirements.

Authorization decisions involve multiple factors beyond user identity. Resource ownership, user roles, contextual information like time or location, and business rules all influence authorization outcomes. For example, a user might be authorized to view their own profile but not others', or an admin might have full access during business hours but read-only access after hours. These nuanced requirements demand sophisticated authorization mechanisms.

Modern APIs must support diverse authorization scenarios. Multi-tenant applications need to ensure users can only access their organization's data. Collaborative platforms require flexible permission models where users can share resources with specific permissions. Microservices architectures need service-to-service authorization to prevent lateral movement in case of compromise. Each scenario requires carefully designed authorization strategies.