MacPlusSupport Office: an invoicing app small businesses sign into with Microsoft (portfolio build). Sign-in uses Microsoft Entra ID (MSAL, PKCE, read-profile permission only), each business sees only its own data, and sign-in tokens are encrypted before they're stored. Invoice numbers can't duplicate or skip: 300 saved at the same instant gave 300 unique numbers, while the common "max + 1" shortcut failed the same test. Built with Next.js, TypeScript and Postgres on Neon, deployed on Vercel. Live at macplussupport-office.vercel.app · Code: github.com/MacSupportPlus/macplussupport-office