🪙 CoinFlow — I Built a Full-Stack Micro-Tasking Platform with GitHub Copilot.

Redwan Shahriar Shubho built CoinFlow, a full-stack MERN micro-tasking platform featuring a real coin economy, Stripe payments, Firebase authentication, and a three-role system for Workers, Buyers, and Admins. The platform allows workers to earn coins by completing tasks and withdraw earnings once they reach 200 coins ($10), while buyers can post tasks with coin rewards and manage submissions through a dashboard. GitHub Copilot assisted in identifying an IDOR vulnerability and recommended database indexes to prevent duplicate submissions and enforce buyer ownership verification.

CoinFlow is a full-stack MERN micro-tasking platform with a real coin economy, Stripe payments, Firebase authentication, and a three-role system for Workers, Buyers, and Admins. Live Demo: coin-flow-peach.vercel.app https://coin-flow-peach.vercel.app GitHub Repo: github.com/redwanshahriarshubho/CoinFlow https://github.com/redwanshahriarshubho/CoinFlow The entire server/ folder had no index.js . Every API call failed with network errors. The frontend looked beautiful but nothing worked. Frontend: React 19, Vite 8, React Router 7, TanStack Query v5, Firebase v12, Stripe.js, Swiper, React Hook Form Backend: Node.js, Express 5, MongoDB native driver , JWT, Stripe SDK Infrastructure: Vercel frontend , Render backend , MongoDB Atlas, imgBB Workers join the platform and get 10 free coins on signup. They browse available tasks, submit completed work, and get paid instantly when approved. Once they hit 200 coins $10 , they can withdraw via bKash, Nagad, Rocket, or Bank Transfer. Buyers post tasks with a coin reward per worker — the total cost is deducted when the task goes live. They review submissions through a dashboard and approve or reject each one. Unused coins are refunded automatically if a task is deleted. Admins see platform-wide stats, manage all users, moderate any task, and approve worker withdrawal requests. | Action | Coins | |---|---| | Register as Worker | +10 free | | Register as Buyer | +50 free | | Post a task | - workers × coins per worker | | Submission approved | +payable amount to worker | | Delete task unused slots | +refund to buyer | | Withdrawal minimum | 200 coins $10 | Exchange rate | 20 coins = $1 USD | One design decision I'm proud of: when a submission is rejected , the task's required workers count is incremented back by 1 so another worker can claim that slot. Without this, a single rejection would permanently block an open position. app.patch "/submissions/:id/reject", verifyToken, verifyBuyer, async req, res = { await submissions.updateOne { id: new ObjectId req.params.id }, { $set: { status: "rejected" } } ; await tasks.updateOne { id: new ObjectId sub.task id }, { $inc: { required workers: 1 } } ; await notifications.insertOne { recipient email: sub.worker email, message: Your submission for "${sub.task title}" was rejected. Keep going , actionRoute: "/dashboard/task-list", time: new Date , read: false, } ; } ; I used Copilot as a sounding board throughout. Describing the coin economy rules in plain English and asking "what could go wrong here?" surfaced edge cases before they became bugs. Copilot flagged an IDOR vulnerability — I wasn't verifying that the buyer making a request actually owned the task. It suggested adding buyer email: req.user.email to every MongoDB mutation query: await tasks.updateOne { id: new ObjectId req.params.id , buyer email: req.user.email }, { $set: { task title, task detail, submission info } } ; Copilot reviewed my schema and recommended the full index set: await users.createIndex { email: 1 }, { unique: true } ; await tasks.createIndex { buyer email: 1 } ; await submissions.createIndex { worker email: 1 } ; await notifications.createIndex { recipient email: 1, time: -1 } ; js const dup = await submissions.findOne { task id, worker email } ; if dup return res.status 400 .json { message: "You already submitted this task" } ; Worker: Browse tasks, full detail page, submit work, paginated history, real-time notifications, withdrawal form Buyer: Post tasks with live cost preview, review submissions via modal, approve/reject with instant worker payout, edit/delete with refund, purchase coins via Stripe, payment history Admin: Platform stats, user management, task moderation, withdrawal approval queue System: JWT + Firebase auth Email + Google OAuth , role-based route guards, imgBB image upload, fully responsive UI Register as a Worker to browse and complete tasks, or as a Buyer to post tasks and review submissions. Test Stripe with card 4242 4242 4242 4242 / any future date / any CVC. Built with React, Node.js, MongoDB, Stripe, and Firebase. GitHub Copilot helped me think through security, edge cases, and performance throughout the build.