Principal Software Engineer

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 tooling Designing the transport and session model (Streamable HTTP), including stateful sessions for progress streaming, subscriptions, sampling, and user elicitation flows Implementing robust OAuth-based authentication and authorisation, integrated with the company's identity provider, with least-privilege, per-request data scoping Designing and operating the edge and gateway layer - Cloudflare Workers and Durable Objects - for token validation, JWKS caching, routing, and session state Defining standards, patterns, and reusable libraries so other teams can build additional MCP servers quickly, consistently, and securely Embedding security and compliance into every layer - this is a high-trust surface over sensitive payment data Driving observability, performance, and reliability across the stack, including logging, tracing, rate limiting, and graceful degradation Mentoring engineers, reviewing designs and code, and acting as a technical leader across a domain that is new, fast-moving, and security-sensitive What they're looking for: 8 to 10 years in software engineering, with a track record of owning systems end to end Deep server-side expertise in Type Script/Node.js

or Python - both are actively used here Strong, practical understanding of the Model Context Protocol - defining tools, resources, and prompts; designing well-typed schemas; writing tool descriptions that drive reliable model behaviour Solid grounding in LLM tool-use and agentic patterns, including how models select and invoke tools, manage context, and handle multi-step interactions Hands-on experience with OAuth 2.0, OIDC, JWT validation, and identity provider integration Experience deploying and operating services at the edge or in serverless environments - Cloudflare Workers, AWS Lambda, Cloud Run, or similar Security-first mindset;

PCI DSS awareness is a strong plus Awareness of AI-specific security concerns - prompt injection, over-broad tool permissions, and safe handling of model-driven actions Comfortable operating as a team of one or scaling up to lead a broader group BS or MS in Computer Science or equivalent practical experience Benefits:
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