Senior Software Security Engineer

📋 Job Overview

Application AI doesn't run in one place anymore. It runs in the browser tab, the desktop app, the agent your engineers kicked off, and the copilot embedded in the tools you already pay for. Harmonic Security governs all of it. Our AI Governance and Control (AIGC) platform sits on the device, inside the interaction, at the moment of action, reading what AI is actually doing (not just the traffic around it) and acting in under 200ms. Security teams get full visibility and control across every AI surface, including the agentic and MCP layer that traditional tools can't see. Their people get to innovate without guardrails slowing them down. We're gaining serious traction at the intersection of AI and cybersecurity, and backed by investors who know the space: N47, Ten Eleven Ventures, and In-Q-Tel. As AI adoption inside the enterprise accelerates, the ability to safely observe, control, and enforce policy in real time isn't a nice-to-have. It's mission-critical infrastructure. That's what we build.

🏢 About Harmonic Security Inc

Harmonic exists to help enterprises adopt AI safely and at scale. We hold ourselves to that same standard. Everyone here actively leverages AI tools to perform their best work — from deep research and writing to building robust processes and automating complex workflows. We expect every new hire to bring a genuine curiosity for AI and a commitment to using it to work smarter, faster, and with greater creativity. For some, this involves tinkering and remaining open to emerging tools; for others, it means architecting entirely new systems with AI at the core. We will be transparent about expectations for every role and provide the tools and support needed for you to thrive.

🎯 The Role

We're looking for a Senior Software Security Engineer to become the authority on our platform's security architecture - and to write the code that embodies it. You'll inherit a platform where the fundamentals of authentication and authorization, secrets and key management, encryption, and multi-tenant data isolation are established, and your job is to sharpen, harden, and evolve them with the depth a dedicated specialist brings that a generalist team can't. You will establish standards and enable the rest of the team to adhere to them. You'll spend the majority of your time writing production code, not producing reports on someone else's.

✅ Key Responsibilities

• Take formal ownership of Harmonic's platform security architecture - authentication and authorization, secrets and key management, encryption at rest and in transit, and multi-tenant data isolation - and evolve it beyond what a generalist engineering team has had the focus to do
• Write production code using our existing languages and tooling (primarily Java, Terraform also Typescript, Rust, Python) to harden and extends these patterns in our core platform.
• Collaborate closely with the platform team, who own our architecture and engineering standards, so that security standards are woven into that shared framework rather than sitting alongside it - you'll shape architectural decisions together, not hand requirements over the fence
• Manage your own backlog of platform security improvements, prioritized independently of the product roadmap
• Run threat modeling and architecture reviews on major new systems and integrations before they ship, so security is designed in rather than retrofitted
• Create a close partnership with the Security team to provide evidence that we are adhering to required standards and ensure they are informed where we go beyond

📌 Required Qualifications

• 6+ years of hands-on software engineering experience, with deep specialization in security architecture rather than general backend development
• Strong working knowledge of Java, and infrastructure-as-code using Terraform and/or OpenTofu
• Experience with AWS and its security fundamentals - IAM, network security, container and secrets management.
• Strong grounding in threat modeling and secure-by-design principles, applied to real architectural decisions rather than theoretical frameworks
• Comfort setting technical standards that other engineers are expected to follow, with the communication skill to bring people along rather than dictate from a distance

⭐ Desirable Experience

• Have built or hardened platform-level security in a SaaS company that faces serious enterprise scrutiny (SOC 2, ISO 27001, customer security questionnaires, or similar)
• Would rather build the fix into the architecture than find the next hole in someone else's code
• Have no patience for security theatre - you measure success by real, shipped improvements to our security posture, not policies, paperwork, or box-ticking that only looks like progress
• Leverage AI tools as an engineer to help you build smarter, faster and better
• Enjoy being the go-to authority on a topic and setting the standard, rather than gatekeeping other people's work
• Are comfortable being the first specialist in this seat, inheriting a solid foundation and having the autonomy - and responsibility - to take it further

🎁 Benefits

London, England
£98K – £115K • Offers Equity • Offers Bonus