Tier 1 Bank - .NET CORE / React / Banking / ArchitectureRole - C# Developer / .NET Core Duration - 6 months with very likely extensionLocation - Hybrid / Canary Wharf - 3 days per week in a Canary Wharf officeRate - 415 p/d inside IR35Tech StackC#.NET CoreSQL / OracleReact / Typescript RoleDeliver, modernise, and support business-critical applications, frameworks and services across our stack (.NET Framework/.NET Core, HTML/CSS/TypeScript/React, Python, SQL Server, Oracle). The role focuses on refactoring legacy systems to reduce technical debt, improve reliability and performance, and embed modern security patterns across the service estate.TasksDesign, build, and maintain server-side and client-side software using .NET (Framework/Core), React/TypeScript, Python, and relational databases (SQL Server, Oracle); contribute to API and UI development, data access layers, and integration points.Refactor and modernise legacy codebases: modularisation, dependency updates, performance tuning, improved observability, and raising automated test coverage within CI/CD.Embed modern security patterns and controls across web services: strong authentication/authorization (e.g., OAuth2/OpenID Connect), token-based access, secure session management, least privilege/role-based access, mTLS/TLS hardening, secure secrets handling, input validation and output encoding (OWASP), dependency vulnerability remediation, and policy enforcement via gateways.Participate in greenfield projects: design and