Senior Software Engineer

Senior Software Engineer (.NET/Multi-Tenant SaaS)We're looking for a Senior Software Engineer to join a project team on a contract basis. The team is building a modern, multi-tenant web platform that lets business customers manage their data and workflows. The solution is a React or Next.js front end backed by a.NET Core API, with single sign-on(SSO) for customer organizations. You'll work alongside the project architect to design and build the platform, set the quality bar for the code the team delivers, and mentor junior and mid-level engineers. You'll also be a key owner of application security and tenant data isolation, so that every customer sees only their own data.What You'll Do:Partner with the architect to design and build a multi-tenant application, including the API, data model and tenant-aware application logic.Design and develop secure, well-documented RESTful APIs in .NET Core that serve the web application and external integrations.Implement authentication and authorization using OAuth 2.0 and OpenID Connect, and integrate SSO with customer identity providers.Enforce tenant data isolation across the API, data layer and application, and verify it through testing and code review.Build and review front-end features in React or Next.js that give customers a clear, efficient experience managing their data.Review code and set standards for quality, maintainability, performance and testing, and make sure delivered work meets the project's requirements and acceptance criteria.Mentor junior and mid-level engineers through pairing, code review and guidance on design decisions.Apply secure development practices (for example OWASP guidance, input validation, least-privilege access and secrets management) and help identify and fix vulnerabilities.Contribute to estimation, backlog refinement and sprint planning, and communicate progress, risks and trade-offs to the team and the client.Help establish and maintain CI/CD pipelines, logging and monitoring, and technical documentation.Document key design decisions and support knowledge transfer to the client's development team as the project progresses.Required Qualifications:6+ years of professional software engineering experience, including significant experience building production APIs in.NET Core (C#).Strong understanding of RESTful API design, including versioning, error handling, pagination and API documentation (OpenAPI/Swagger).Experience with relational databases (SQL Server preferred), including data modeling, query tuning and Entity Framework Core.Working knowledge of OAuth 2.0 and OpenID Connect, including token-based authentication, scopes and claims, and role- and policy-based authorization.Solid understanding of multi-tenancy concepts, such as tenant isolation strategies (shared vs. separate schemas or databases), tenant resolution and per-tenant configuration.Demonstrated ability to build secure applications and protect customer data, including protecting against common web vulnerabilities.Experience writing automated tests (unit and integration) and working with source control, code review and CI/CD.Experience mentoring or technically guiding other engineers.Proven ability to get productive quickly in an unfamiliar codebase and work independently in a remote setting.Strong written and verbal communication skills, and comfort collaborating with architects, designers, project managers and client stakeholders across distributed teams.Preferred Qualifications:Located in or near the Grand Rapids, Michigan area.Experience with React or Next.js, including TypeScript, component-based design and state management.Experience with SCIM or automated user provisioning, and with role mapping from identity provider groups.Prior work on multi-tenant SaaS products, including per-tenant branding or configuration.Familiarity with Azure services, Azure DevOps or other CI/CD tooling, and applications hosted on Windows Server/IIS.Experience with audit logging, observability (logging, monitoring, correlation IDs) and performance profiling.Experience designing and building APIs for partner or third-party integrations.Experience replacing or modernizing legacy systems.Prior consulting or contract engagements where you joined a team mid-stream and handed work off to a client team.Experience working in an Agile/Scrum environment.