Senior C# IAM Developer - Auth0, CIAM, AWS - Outside IR35

Senior C# IAM Developer - Auth0, Identity & Access Control, AWS OUTSIDE IR35

Contract: 8 monthsRate: £700 - £750 OUTSIDE IR35Location: 100% remote

The Role:

Working for a global, market leading B2B SaaS business, youll lead the design and implementation of secure, identity-driven backend services in a modern C#/.NET environment. Your work will centre on authentication, authorization, and secure event-driven architectures. Youll own our Auth0 integration end-to-end, ensuring our platform meets strict security, compliance, and reliability standards.

This is a role for someone who thinks deeply about threat models, defence-in-depth, and secure-by-default engineering.

What Youll Do:

• Architect and implement secure backend services in C# & .Net
• Own and evolve our Auth0 identity platform: tenant configuration, flows, hooks, rules, MFA, RBAC
• Design and maintain token-based security models (OIDC, OAuth2, JWT lifecycle, refresh strategies)
• Build secure event-driven and serverless components (AWS Lambda, SNS/SQS, EventBridge)
• Lead secure coding practices, code reviews, and threat modelling sessions
• Work closely with product and platform teams to ensure security is embedded from design to deployment
• Improve observability around authentication flows, anomaly detection, and abuse prevention
• Contribute to internal security standards, policies, and incident response readiness

What You Bring:

• 10+ years experience building production systems in C# & .NET
• Deep knowledge of Auth0 (Actions, Rules, Hooks, Universal Login, MFA, RBAC, custom claims)
• Solid understanding of OAuth2, OIDC, SAML, JWT, and modern identity patterns
• Experience with AWS serverless (Lambda, API Gateway, DynamoDB, EventBridge)
• Strong grasp of secure coding principles: input validation, secrets management, least privilege, secure session/token handling
• Ability to design and review threat models for distributed systems
• Comfortable working in high-autonomy, high-ownership environments
• Bonus: experience with Terraform, CI/CD security, or penetration testing

Why Join Us:

• Work on a greenfield platform where security is a first-class concern, not an afterthought
• High-impact role with architectural ownership
• Modern stack, modern identity tooling, modern engineering culture
• Competitive compensation, flexible working, and a team that values technical excellence

Contract: 8 monthsRate: £700 - £750 OUTSIDE IR35Location: 100% remote