Principal Software Engineer - Security

What You'll Do As a Principal Software Engineer - Security, you will help set the technical direction for Radiant's security capabilities across the cloud platform and infrastructure, leading the design and delivery of the systems that underpin them. You'll work across identity, access control, secrets, network security, platform hardening, auditability, and compliance controls. You'll partner closely with product, infrastructure, SRE, networking, security, and compliance teams, and with customers on their most demanding security requirements. This is a hands-on technical leadership role focused on making security embedded, scalable, automated, and easy to consume across the platform, through architecture, code, and the standards other teams build on. Key Responsibilities Set the technical vision and architecture for security systems and platform capabilities, and lead their design and implementation. Design and build core security services across IAM, RBAC, workload identity, secrets, encryption and key management, audit logging, network controls, and policy enforcement. Translate product, customer, and regulatory requirements into robust architectures, APIs, and technical designs, working closely with the Security Product Manager. Drive automation of policy enforcement, configuration hardening, detection, remediation, and software supply chain security. Ensure strong tenant isolation and least-privilege access across the control plane and network and data plane. Act as a senior technical voice in enterprise customer security reviews, audits, and incident response. Raise the security engineering bar across the organisation through mentoring, code review, and technical standards. Your Profile Strong hands-on engineering skills in one or more systems languages such as Go or similar. Extensive experience building and operating large-scale distributed systems, with significant depth in cloud and network security, IAM, or security infrastructure. A track record of technical leadership at staff or principal level, including setting direction across multiple teams and delivering complex, high-stakes systems. Deep technical expertise across: Identity & access: IAM, RBAC/ABAC, OAuth 2.0, OIDC, SAML, SSO, federation, mTLS, workload and service identity Security controls: applied cryptography, encryption at rest and in transit, secrets management, KMS/HSM, key rotation, policy engines Infrastructure: Kubernetes internals, containers and runtime isolation, cloud networking, compute, storage Security operations: audit logging pipelines, detection engineering, vulnerability management, incident response Automation: policy-as-code, infrastructure-as-code, CI/CD security, software supply chain (signing, SBOMs, provenance) Hands-on experience with technologies such as Vault, OPA/Gatekeeper, SPIFFE/SPIRE, Kubernetes admission control and security tooling, Sigstore, SIEM platforms, cloud KMS, or similar. Deep understanding of multi-tenancy, least privilege, zero-trust architecture, threat modelling, and shared-responsibility models. Familiarity with compliance frameworks such as SOC 2 or ISO 27001, and how they translate into technical controls. Able to balance security, performance, reliability, operational complexity, and developer experience. Excellent written and verbal communication, including clear design documents and explaining complex trade-offs to technical and non-technical audiences. What You Bring Security mindset: Think like an attacker and design systems that fail safely, without making them painful to use. Engineering excellence: Write and review code that sets the standard for correctness, reliability, and maintainability. Architectural judgement: Make sound long-term decisions on systems that are hard to change once built. Technical leadership: Influence direction across teams without relying on authority, and grow the engineers around you. Systems thinking: Understand how controls interact across the full cloud platform, from network and infrastructure up to APIs and user experience. Ownership: Drive security capabilities from design through production, operation, and continuous improvement. Qualities we look for: Set the standard: Every single day, you spot opportunities to constructively shake things up Inspire the change: There's no blueprint for the future. You'll embrace challenges and change You're real and you're true to yourself: We cherish and celebrate diversity so you'll feel right at home whoever you are and whoever you're talking to, you treat everyone the same. Why should you join us? What sets us apart is our blend of modern technology, competitive benefits, and an open, welcoming work culture that enables our people to thrive. Here are just some of the great things you can expect from us: 25 days of annual leave A culture that emphasises results over hierarchy, process & ego: we place great emphasis on the quality, ingenuity and creativity of work. Open communication, regular feedback: we value smooth collaboration, direct and actionable feedback, and believe that leading with empathy and a growth mindset makes us better together. Learning Time: we all have dedicated learning time to focus on new skills, projects or interests that lay outside of your day-to-day job. Health & Wellbeing: we want everyone to feel healthy and happy, so we offer private medical insurance via Bupa. Cycle to Work Scheme: we're committed to building a sustainable business, so we encourage cycling to work. Gympass subscription to a variety of gyms and wellbeing apps Participation in the company shares program Enhanced parental pay & leave Our process: Talent screen → Hiring Manager → Technical interview (two Principal Engineers) → Whiteboard Session → Final. Company Overview: Radiant is redefining how AI infrastructure is built. We design and operate AI-native cloud platforms engineered for sovereignty, performance, and scale. Our infrastructure powers GPU-native workloads, multi-tenant control planes, and high-performance AI systems designed for the most demanding environments. We are not building a generic cloud. We are building purpose-built AI infrastructure — from powered land, to compute, to software. As we scale, we're building this organisation from the ground up. We're looking for people who'd rather build the playbook than inherit one — who are comfortable doing the work themselves as well as directing others, and who can adapt as fast as our strategy does. This is a startup model: attitude and adaptability matter more to us than years of experience or the size of the team you've previously managed.