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✦ Ayush Kumar Singh — Full-Stack / Backend Engineer MERN · Payments · Auth & Security open to work — Bhopal, India
my engineering sketchbook ✎

Ayush Kumar Singh

I build the payments, auth & security pages of the story — the ones that can't have typos.

Associate Software Engineer at Pabbly. I reconcile payment gateways that disagree with each other, rotate refresh tokens without logging anyone out, and chase connection leaks at 2am. Systems where "mostly works" isn't a passing grade — that's my favourite kind.

Flip to my projects ✦ Say hello
Hand-drawn portrait sketch of Ayush Kumar Singh
that's me, allegedly
400+
LeetCode problems
148
REST endpoints, one app
3
payment gateways tamed
~ the day jobs ~

Where I've worked

two stops so far — both about money moving correctly

Pabbly · Associate Software Engineer

Nov 2025 — now

on-site · Bhopal · payments team

  • ✓ Built a payment reconciliation system across 3 gateways (Stripe, Razorpay, PayPal) using concurrent cron jobs with fair-share scheduling — no merchant starves the others.
  • ✓ Migrated PayPal recurring billing to the Subscriptions API with full backward compatibility and zero disruption to live subscriptions.
  • ✓ Resolved a production MongoDB connection exhaustion incident via connection pooling and graceful shutdown, and removed redundant checkout API round-trips.
  • ✓ Shipped multi-key API auth with RBAC, custom domains and transaction-fee billing — auto-migrated 100% of single-key users with zero downtime.
Stripe Razorpay PayPal MongoDB

Bluestock Fintech · Full-Stack Intern

Apr — May 2025

remote · fintech dashboards

  • ✓ Developed an IPO analytics dashboard in React, Node.js, Express and MongoDB serving data across 10+ active IPO listings.
  • ✓ Designed 15+ REST endpoints with JWT auth and role-based access control; cut query response time with compound indexes and projection queries.
React Node.js Express MongoDB
~ nights & weekends ~

The project pages

a suspicious number of webhooks were harmed in the making

Sketch of the Scribble writing platform — editor with session and webhook panels
scribble — the writing machine

Scribble

May 2026 →

writing platform · MERN · security-first

  • ✦Hardened session auth: httpOnly-cookie JWTs, refresh-token rotation with SHA-256 reuse detection, per-device instant revocation.
  • ✦Outbound webhooks across 11 event types — HMAC-SHA256 signing, SSRF/DNS-rebinding protection, retry-with-backoff auto-disable.
  • ✦Server-side RBAC over 3 workspace roles, 90-day audit trail, race-safe analytics via atomic upserts.
MERN JWT Web Locks API
GitHub Live
Sketch of the TransitOps fleet dashboard with a serverless AWS architecture doodle
transitops — buses in the cloud

TransitOps

Jul 2026 →

fleet operations · serverless AWS

  • ✦MERN fleet app deployed serverless — Express as a Lambda behind API Gateway, one CloudFront origin serving the SPA and proxying /api/* from OAC-locked S3.
  • ✦Whole stack as infrastructure-as-code with AWS SAM, plus GitHub Actions running sam deploy, S3 sync and CloudFront invalidation.
  • ✦Warm-Lambda MongoDB connection pooling across a 42-endpoint API — warm invocations reuse an open connection.
AWS SAM Lambda MongoDB
GitHub Live
Sketch of the Skill Path course marketplace with checkout and AI key delegation notes
skill path — 148 endpoints of it

Skill Path

Jan — Jun 2026

course marketplace · Stripe · AI keys

  • ✦Multi-role marketplace spanning 148 REST endpoints and 19 models, with Stripe Checkout, signature-verified webhook enrollment and PDFKit invoicing.
  • ✦Per-course AI key delegation across OpenAI, Gemini and Anthropic — AES-256-GCM encrypted key storage, per-student blocks, read-only conversation auditing.
  • ✦JWT auth, course-ownership middleware, Google OAuth 2.0 server-side code exchange, admin impersonation for support.
Stripe OAuth 2.0 AES-256-GCM
GitHub Live
~ everything in the pencil case ~

What's pinned to the board

Backend
Node.js · Express.js · Sails.js · REST APIs
Databases
MongoDB · Mongoose · MySQL · PostgreSQL
Frontend
React.js · Tailwind CSS · Zustand · Vite
Languages
C++ · JavaScript · Java · SQL
Payments
Stripe · Razorpay · PayPal · webhooks
Cloud & CI
AWS · GitHub Actions · Git
Security
JWT · OAuth 2.0 · RBAC · AppSec
Foundations
DSA · OOP · MVC · Distributed Systems
~ the report card ~

Proof it's going okay

B.Tech, Computer Science & Engineering — CGPA 8.6 / 10. Four years of algorithms, OS fundamentals and far too much chai.

V
Vellore Institute of Technology
Aug 2022 — Mar 2026

400+ problems solved on LeetCode — ranked among the top coders on a campus of 15,000+ students.

★
Competitive programming
leetcode.com/ayushsingh03
~ last page ~

Got something that needs
building — or breaking?

Payments, auth, a webhook that misbehaves at 2am — drop a note below and I'll write back.

~ note slip ~

Leave me a note ✎

singhayush.sa81@gmail.com +91 93054 54214 GitHub LinkedIn LeetCode Resume