Lambda authorizers are AWS Lambda functions. With custom request authorizers, you will be able to authorize access to APIs using a bearer token auth strategy such as OAuth. When an API is called, API Gateway checks if a Lambda authorizer is configured, API Gateway then calls the Lambda function with the incoming authorization token. You can use Lambda to implement various authorization strategies (e.g. JWT verification, OAuth provider callout) that return IAM policies which are used to authorize the request. If the policy returned by the authorizer is valid, API Gateway will cache the policy associated with the incoming token for up to 1 hour.