Understanding Custom Authorization Mechanisms in Amazon API Gateway and AWS AppSync

AWS provides Lambda-based authorization capabilities for both API Gateway and AppSync, each designed to secure different API paradigms, highlighting their complementary roles and the confidence they inspire in combined security potential. Amazon API Gateway positions Lambda authorizers as a security checkpoint between incoming requests and backend integrations — whether Lambda functions or HTTP endpoints. The authorizer validates credentials, executes custom authentication workflows, and produces IAM policy documents that explicitly grant or deny access. These policies guide API Gateway’s decision to forward or reject requests to backend services.