Senior Software Engineer (.NET/Multi-Tenant SaaS)

B5 Recruiting•Minneapolis, MN

About The Position

The Senior Software Engineer will join a project team on a contract basis to build a modern, multi-tenant web platform that enables business customers to manage their data and workflows. The platform uses a React or Next.js front end backed by a .NET Core API and supports single sign-on for customer organizations. Working alongside the project architect, the engineer will help design and build the platform, set code quality standards, mentor junior and mid-level engineers, and own key aspects of application security and tenant data isolation. The role also contributes to delivery planning, CI/CD, observability, technical documentation, and knowledge transfer to the client's development team.

Requirements

At least 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 with OpenAPI/Swagger.
Experience with relational databases, preferably SQL Server, 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, including tenant isolation strategies, tenant resolution, and per-tenant configuration.
Demonstrated ability to build secure applications and protect customer data against common web vulnerabilities.
Experience writing automated unit and integration tests and working with source control, code review, and CI/CD.
Experience mentoring or technically guiding other engineers.
Ability to become productive quickly in an unfamiliar codebase and work independently in a remote setting.
Strong written and verbal communication skills and ability to collaborate with architects, designers, project managers, and client stakeholders across distributed teams.

Nice To Haves

Located in or near Grand Rapids, Michigan.
Experience with React or Next.js, including TypeScript, component-based design, and state management.
Experience with SCIM or automated user provisioning and 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 involving joining a team mid-stream and handing work off to a client team.
Experience working in an Agile/Scrum environment.

Responsibilities

Partner with the architect to design and build the multi-tenant application, including its API, data model, and tenant-aware application logic.
Design and develop secure, documented RESTful APIs in .NET Core for 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 React or Next.js front-end features for customer data and workflow management.
Review code and establish standards for quality, maintainability, performance, and testing; ensure delivered work meets project requirements and acceptance criteria.
Mentor junior and mid-level engineers through pairing, code review, and guidance on design decisions.
Apply secure development practices, help identify and fix vulnerabilities, and protect customer data.
Contribute to estimation, backlog refinement, and sprint planning; communicate progress, risks, and trade-offs to the team and client.
Help establish and maintain CI/CD pipelines, logging, monitoring, and technical documentation.
Document key design decisions and support knowledge transfer to the client's development team.