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 & Experience
Strong experience developing backend applications using C#/. NET, with Java also considered.
Expertise building and supporting REST APIs within microservices-based environments.
Strong understanding of identity, authentication, and authorisation concepts.
Experience working with OAuth2, JWT, and OpenID Connect.
Knowledge of distributed systems and graph modelling principles.
Ability to design and develop scalable platform services and developer-facing SDKs.
Experience integrating systems with Kubernetes, API Gateway technologies, or Service Mesh environments.
Understanding of policy-based access control, RBAC, ReBAC, ACL, or policy-as-code frameworks.
Exposure to technologies such as Neo4j, OpenFGA, SpiceDB, OPA, Redis, or Kafka would be beneficial.
How to Apply
If you are a Senior C# Backend Engineer with experience in identity, authorisation, distributed systems, and cloud-native architectures, apply today to learn more about this exciting contract opportunity.