Senior C# IAM Developer - Auth0, CIAM, AWS - Outside IR35 at Smart Sourcer Limited, City of London, £Contract Rate
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What you'll 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 they're looking for
- 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
Nice to have
- Bonus: experience with Terraform, CI/CD security, or penetration testing
Summarised by NextRaise from the employer’s description, which follows in full below.
Full description from employer
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, you’ll 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. You’ll 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 You’ll 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
Company
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