Lakshay Mahajan
Experience
Backend Developer
Internware
Delhi, India
Engineered event registration system handling 800+ registrations and 500+ paid transactions per event, integrating Cashfree API with Express and Mongo DB. Identified and fixed a client-side payment vulnerability, redesigning flow with server-side validation and webhook verification to ensure transaction integrity. Implemented reservation-based registration with TTL to prevent seat hoarding and auto-expire inactive bookings.
Built dynamic cart system for multi-day events, enabling tier modification and post-purchase session additions without admin intervention. Developed coupon management system allowing non-technical teams to manage discount codes with expiry controls. Developed permission-based admin dashboard with real-time attendance tracking, ensuring a single source of truth.
Education
Guru Gobind Singh Indraprastha University
Bachelor of Computer Application
GPA: 9.1/10.0
Skills
Node.jsExpress.jsTypeScriptMongoDBSQLPostgresRESTful APIJWT/OAuth 2.0DockerIdempotencyPayment Gateway IntegrationRBACCI/CDGitLinuxPostmanBcryptZod
PROJECTS
Authentication Service + Resource Hub
Offloaded file transfers from the server using MinIO presigned URLs; enforced MIME type and size constraints at the storage layer before files reach the application. Implemented webhook-based upload confirmation with shared secret verification; used MongoDB TTL index to auto-expire incomplete uploads after 24 hours.
Architected decoupled authentication service with async email delivery via AWS SNS/SQS/Lambda; added Dead Letter Queue with CloudWatch alarms and 3-retry strategy for failures. Built JWT (RS256) auth with httpOnly cookies, Google OAuth 2.0, and rate limiting.
FinTech Core — Transaction-Safe Backend System
Implemented per-user mutex locking to prevent race conditions and double-spending in concurrent transactions. Designed idempotent API layer ensuring duplicate requests do not result in duplicate financial operations. Built write-through balance caching, reducing redundant database aggregation queries.
Prevented user enumeration attacks by equalizing authentication response timing using bcrypt fallback strategy. Implemented RBAC with scoped access control and enforced soft deletes (deletedAt) to maintain audit trails.
TECHNICAL WRITING
Published technical deep-dives
Payment Architecture, OAuth 2.0, SSL Certificates, UPI Systems, Access & Refresh Tokens.