Principal Platform Engineer FULLY REMOTE ACROSS UK AND IRELAND Our client is a fast-scaling fintech building the next generation of payment infrastructure. They're merchant-first, engineering-led, and genuinely obsessive about outcomes over process. Small teams, real autonomy, hard problems.They're hiring a Principal Platform Engineer to own the design and delivery of a suite of Model Context Protocol (MCP) servers - the trusted, governed gateway between AI agents and their core payments platform.This is a hands-on principal role. You'll set technical direction and write production code, not just review it.What you'll be doing:Owning the architecture and delivery of MCP servers that expose platform data and capabilities to AI agents and internal developer toolingDesigning the transport and session model (Streamable HTTP), including stateful sessions for progress streaming, subscriptions, sampling, and user elicitation flowsImplementing robust OAuth-based authentication and authorisation, integrated with the company's identity provider, with least-privilege, per-request data scopingDesigning and operating the edge and gateway layer - Cloudflare Workers and Durable Objects - for token validation, JWKS caching, routing, and session stateDefining standards, patterns, and reusable libraries so other teams can build additional MCP servers quickly, consistently, and securelyEmbedding security and compliance into every layer - this is a high-trust surface over sensitive payment dataDriving observability, performance, and reliability across the stack, including logging, tracing, rate limiting, and graceful degradationMentoring engineers, reviewing designs and code, and acting as a technical leader across a domain that is new, fast-moving, and security-sensitiveWhat they're looking for:8 to 10 years in software engineering, with a track record of owning systems end to endDeep server-side expertise in TypeScript/Node.js or Python - both are actively used hereStrong, practical understanding of the Model Context Protocol - defining tools, resources, and prompts; designing well-typed schemas; writing tool descriptions that drive reliable model behaviourSolid grounding in LLM tool-use and agentic patterns, including how models select and invoke tools, manage context, and handle multi-step interactionsHands-on experience with OAuth 2.0, OIDC, JWT validation, and identity provider integrationExperience deploying and operating services at the edge or in serverless environments - Cloudflare Workers, AWS Lambda, Cloud Run, or similarSecurity-first mindset; PCI DSS awareness is a strong plusAwareness of AI-specific security concerns - prompt injection, over-broad tool permissions, and safe handling of model-driven actionsComfortable operating as a team of one or scaling up to lead a broader groupBS or MS in Computer Science or equivalent practical experienceBenefits:Work From HomeWHJS1_NI