How to Build a Secure Tax Payment Platform

Before you ship a vibe-coded app, run this security checklist. Vibe coding makes it easy to ship a working app. It does not make that app secure, private, or ready for real users. ☑ Know what user data you collect Add a privacy policy. Know where the data lives, who can access it, and how users can delete it. ☑ Lock down your database For Supabase, enable Row Level Security and set least-privilege grants for every exposed table. Test what anonymous and authenticated users can read, create, update, and delete. ☑ Attack the authentication flow Try the wrong password several times. Reuse a verification link. Reset a password for an unknown email. Register an existing email. The failure path finds bugs the demo never shows. ☑ Validate every input on the server Client-side validation improves the interface. Attackers can bypass it and call your API directly. ☑ Keep secrets off the client Anything sent to the browser can be inspected. API keys, service credentials, and privileged database keys belong on the server. ☑ Check for data leaks Inspect frontend bundles, API responses, logs, error messages, and committed files. Your API should return only what the screen needs. ☑ Add abuse controls Rate-limit paid endpoints. Protect public forms with a bot challenge such as Cloudflare Turnstile, and verify its token on the server. ☑ Review access, injection, and configuration risks Use the OWASP Top 10 as a starting point. Do not treat an AI security prompt as the final review. ☑ Test the deployed app Production headers, environment variables, permissions, and logging can differ from local development. AI can help you build and review faster. But it cannot accept the legal bill, rotate a leaked key, or explain exposed customer data. Shipping speed is useful only when the system survives contact with real users. If this helps, hit the ♻️ reshare button so another builder checks before launching. I'm Shrey Shah & I talk about harness engineering.

Payments-Grade Agents This is the 5th post in a series on “payments-grade” agents. This post focuses on the trust framework that forms the basis for payments agents. What are trust framework pillars, and why are they important? --- Trust Is the Currency of Payments Agents In payments, trust is everything. Without it, adoption of agents will be slow, cautious, and fragmented. With it, agents can securely handle money, contracts, and compliance at scale. But trust doesn’t come from one feature. It comes from layers of capability, each reinforcing the other. Leave one layer out, and the system is compromised. Fortunately, we don’t need to reinvent the wheel. Decades of proven practices—identity management, security standards, certification programs—can be reused and applied directly to agents. Here are the six pillars of a Payments Agent Trust Framework: 1/ Agent Identity Every agent must have a verifiable identity, just like every employee in an organization. That identity is anchored in the organization’s book of record, serving as the foundation for authentication, authorization, and accountability. 2/ Authentication & Authorization Identity alone is insufficient. Once authenticated, agents must be governed by roles and permissions that define what they are allowed—and not allowed—to do. 3/ Basic Security Agents must come with enterprise-grade security built in, including mutual TLS (mTLS), OAuth2, and integration with existing identity systems. This ensures that communications are encrypted, identities are verified, and only trusted entities can exchange information. 4/ Transparent Purpose and Policies Agents cannot be black boxes. Each must declare its purpose, task fulfillment approach, and governing policies. Transparency builds confidence (and opacity erodes it). 5/ Zero-Trust Model Agents should begin with no access to data, systems, or tools. Nothing is assumed; everything must be granted explicitly by the agent’s owner. 6/ Federated Certification Trust also requires external validation, or “certification”. Just as physical products are certified for safety and compliance, agents should be certified to their purpose and policies. And we should learn and aopt approached used for decades by organizations like the Canadian Standards Association or Underwriters Lab (in US). cc: Paul Andrusyshyn, Maya Nahlé, M.Sc., Andrew Higgins, Abdulah El Tarazi, Reggie Kartha, Sridhar (Sri) Narayanan, Graham Steele, Alex Dunkerley, James Hutton, Joseph Kim, Catherine Martin #Payments #AutonomousAgents #AgenticAI #AgenticMesh #Age #ISO20022 #DigitalTransformation #Fintech #OperationalEfficiency #TrustFramework #FinancialServices #SWIFT #NACHA #PSD2 #EnterpriseAI #LLM

In my pre-Bain life I did a fair amount work focused on making government payments accessible, easy to use, and modern. Recent DOGE efforts draw attention to the need for improvement, but I fear the result will be chaos. But it is a wake-up call for how we can do better. Payment enabled eGov solutions ought to be seamless, secure, and efficient. Instead, they are often a mess of inefficiency, manual processes, and legacy systems that frustrate both citizens and businesses. Governments can (and must) do better. Based on my work with municipal, state/provincial, and national agencies here in the U.S. and abroad, here are my suggestions: 1️⃣ Go digital—but do it right Paper checks and manual processing should be relics of the past. e-payments reduce costs, increase speed, and improve security. But modernization needs to be done strategically, not as a rushed power grab. The Government Finance Officers Association (GFOA) stresses the importance of clear policies to ensure smooth implementation. 2️⃣ Prioritize security and access controls One of DOGE’s biggest missteps was attempting to override Treasury’s existing safeguards. To retain trust, governments need to implement robust security protocols, multi-factor authentication, and access restrictions to prevent unauthorized use of sensitive financial data. 3️⃣ Build transparency and accountability Every payment should be auditable, and every decision should be accountable. Establishing clear oversight mechanisms prevents fraud and ensures public trust. Solutions like real-time transaction monitoring and transparent reporting help keep everyone honest. 4️⃣ Leverage APIs and interoperability Government payment systems should integrate seamlessly with banking infrastructure, tax agencies, and social services. APIs allow for better data exchange, reducing processing delays and ensuring more efficient fund distribution. 5️⃣ Ensure 24/7 availability Citizens rely on government payments for essentials. Government agencies can take advantage of round-the-clock payment rails. But real time payment infrastructure isn't enough. Gov agencies need redundancy measures in place to prevent downtime and must streamline internal processes to ensure that benefits and refunds aren’t delayed by bureaucratic inefficiencies. 6️⃣ Use smart reporting and analytics Robust data analytics can help detect anomalies, optimize agency cash flow management, and prevent fraud. Government entities should invest in AI-driven insights to improve forecasting and decision-making. The Path Forward Government payment modernization isn’t just about technology—it’s about trust. DOGE’s overreach highlights the dangers of prioritizing speed over thoughtful execution. The alternative? A strategic, well-governed shift toward digital, secure, and interoperable payments that serve the public good. The stakes are too high to get this wrong. Let’s make sure we get it right. (photo is me in Islamabad back in 2016)

Building a Payment Service from Scratch - What I Learned as a Founder When we started building the payment system at takeUforward, I thought it would be simple, just integrate Razorpay/Paypal and move on. But once we went deeper, it turned into a full product within a product. Payments are about reliability, data integrity, and how gracefully your system behaves under pressure. Here’s what we learned 👇 - Don’t build only for “plans”, design for plan entities in your schema so upgrades/bundles/emi’s/future standalone offerings are easier to integrate - Support multiple validity periods within the same flow. - Implement an Adapter Pattern so gateways like Razorpay, PayPal, or Stripe can be swapped without touching business logic. - Keep a transaction_id as the single source of truth and design every API around it (create, capture, refund, audit) - Log everything, and store gateway response for future auditing - Ensure idempotency for every payment and refund API - a single retry shouldn’t double charge a user - Run all external calls async using background jobs or message queues to avoid blocking the user flow - Integrate refund callbacks with GST reversal logic to maintain accurate tax credits - Implement signature validation and webhook verification to avoid spoofed callbacks - Support EMI and split payments, each transaction linked via a parent-child hierarchy - Build monitoring dashboards for transaction latency, failure rates, and P95 response times - Use feature flags to roll out new gateways or payment logic gradually - Integrate third party sales - Integrate other product sales on our platform, manage taxes for them. These things sound overkill at the start, until you hit scale and realize why systems like Stripe and Razorpay obsess over these details. 💡 Check out TUF+ - we’ve covered OOPs/LLD over there, along with everything needed for Interview Preparation. It’s your one-stop interview prep platform for DSA, LLD, Core CS and more. Use code STRIVER to get the maximum discount, valid for the next few hours only ⏰

A junior building a microservice with AI in an afternoon is no longer surprising. But the interview starts after the demo works. A payment service is the perfect example. User clicks Pay. Payment provider charges the card. Your service crashes before updating the order status. Now what? – Did the user pay? – Is the order confirmed? – Should we retry? – Will retrying charge them twice? – What does customer support see? – What happens if the provider callback arrives late? That is where system design begins. Btw, if you’re preparing for Senior to Principal-level system design interviews, I’ve put together 90+ fundamentals like this into a guide. You can check it out here: puneetpatwari.in Here is how I would discuss this in an interview: [1] First, define the invariant For payments, the invariant is simple: One logical payment attempt should create at most one successful charge. Everything else should protect that rule. So before talking about Kafka, Redis, workers, or retries, I would clarify the correctness requirement. [2] Use idempotency If the client retries because of a timeout, the backend should not treat it as a new payment. It should use an idempotency key tied to the order and user. Same key, same logical payment attempt. If the first attempt already succeeded, return the original result. If the same key comes with a different payload, reject it. [3] Treat payment as a state machine A payment is not just success or failure. It can be: created → pending → authorized → captured → failed → refunded When the service crashes halfway, the system should resume from the last known state instead of guessing. That means storing state durably before calling external systems, and reconciling with the payment provider when state is unclear. [4] Handle failure modes explicitly Good interview discussion includes: - service crash after provider charge - duplicate webhook from provider - retry from client - payment timeout - order service unavailable - database write failure - message queue delay - refund or reconciliation path This is production reality.