William Duhe enhanced the phuhung273/aws-cdk repository by implementing support for custom security groups in S3 asset deployments. He extended the BucketDeploymentProps interface to accept optional securityGroups, ensuring these were correctly integrated into the Lambda execution path. This approach enabled granular network security controls, allowing users to meet stricter security and compliance requirements for asset deployments. William maintained backward compatibility throughout the changes and expanded both unit and integration test coverage to validate the new logic. His work, primarily using TypeScript and AWS CDK, also included updating documentation to guide users on configuring VPC, subnets, and security groups effectively.