This report details my experience working in Application Security at Shopify, specifically focusing on the critical task of securing the ecosystem of first and third-party applications submitted to the Shopify App Store. As a prominent e-commerce company, Shopify must prioritize the protection of customer data by proactively addressing security vulnerabilities. The projects I worked on dealt with the challenge of building a robust platform that prevents attacks while also providing a smooth user experience for the ecosystem developers interacting with our product.