Senior C# Backend Engineer

Senior C# Backend Engineer £550 - £650 per day London 2 days per week onsite This is an opportunity to join a greenfield platform programme focused on building a modern identity and authorisation capability from the ground up. You will help shape core platform services that will be consumed across a wider ecosystem of AI-native applications, data services, and microservices. The Company They are a technology-led organisation investing in a next-generation platform designed to support complex enterprise-scale products and services. The programme is in its early stages, giving contractors the opportunity to influence architecture, engineering standards, and platform capabilities. The project is expected to be a long-term initiative, with initial contractors playing a key role in its evolution and future growth. The Role and Deliverables Develop and maintain authorisation SDKs, Policy APIs, identity services, and authorisation microservices. Design and implement secure identity and access management capabilities using OAuth2, JWT, and OIDC standards. Build authorisation models including RBAC, ReBAC, ACL, policy evaluation, delegated administration, and permission inheritance. Develop integrations with API Gateway, AI Gateway, Kubernetes, and Service Mesh technologies. Contribute to distributed systems design, graph-based relationship modelling, and scalable microservices architecture. Create automated tests, authorisation regression suites, and performance testing frameworks to ensure platform reliability. Your Skills