Principal Backend Software Engineer - Auth & Identity in London

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 our platform and expand our engineering organisation, we are looking for leaders who can build strong teams, uphold high standards, and deliver reliably at pace.

What You’ll Do:

• As a Software Engineer at Radiant, you’ll be a hands-on technical leader, driving the design and development of our most critical systems, including our GPU orchestration layer, inference-serving infrastructure, and core platform APIs.
• You’ll set the standard for engineering excellence across the team, working closely with other principal engineers to align on strategy and drive technical leadership.
• You’ll partner with peers in infrastructure and machine learning to deliver high-performance AI systems, and mentor engineers across multiple squads.
• Design and build proprietary identity federation, authentication, and authorization infrastructure that securely connects cloud services, customer tenants, and external identity providers (Azure AD, Okta, Google Workspace, etc.) across the Radiant AI cloud platform.
• Architect and develop native IAM, federation, and role-based access control systems that enable secure interoperability between cloud services, customer tenants, and third-party identity providers.
• Build foundational identity federation and authorisation technologies beyond cloud-managed integrations.
• Develop and maintain authentication and authorization services, including OAuth2, OIDC, SAML, and custom token-based solutions.
• Collaborate on backend engineering design efforts, including architecture reviews and system evolution strategies.
• Maintain high standards for backend code quality, observability, and maintainability through code reviews and engineering best practices.
• Identify and resolve security issues, performance bottlenecks, or reliability challenges within your domain.

What You Bring:

• Proven expertise in Golang and cloud-native backend development.
• Deep knowledge of OAuth2, OIDC, SAML, JWT.
• Understanding of cryptography fundamentals (TLS, PKI, key rotation, secrets management).
• Experience implementing RBAC and Zero-Trust principles.
• Experience with Postgresql or other RDMS databases.
• Experience designing scalable, low-latency microservices for authentication and authorization.
• A bias for action, accountability, and leading by example.

Preferred Skills (Nice to Have):

• Experience with Kubernetes and cloud-native services.
• Experience with Auth0 and/or Keycloak.
• Familiarity with confidential computing and zero-trust networking.
• Knowledge of compliance frameworks like SOC2, HIPAA, FedRAMP, or GDPR.

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: we value your peace of mind. With 30 days off (excluding public holidays) and access to mental health resources, we make sure you're as strong mentally as you are professionally.
• 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.

Diversity, Equality, Inclusion and Belonging: We are an equal opportunity employer and we strive to reduce unconscious bias throughout our hiring process. All applicants will be considered for employment without attention to ethnicity, religion, sexual orientation, gender identity, family or parental status, national origin, veteran, neurodiversity status or disability status. To ensure our recruitment processes provide an equal opportunity for all applicants to succeed, we encourage you to let us know if there are any adjustments that we can make.