Senior Software Engineer

Senior Software Engineer, JavaFusionAuth is a fast-growing startup and leading provider of customer identity and access management (CIAM) software headquartered in Denver, Colorado. Our mission is to make authentication and authorization simple and secure for every developer. Our product helps businesses securely manage customer identities and access, ensuring a safe user experience for some of the largest brands in the world. We are committed to delivering exceptional value and satisfaction to our clients through top-notch service and support. With a great team and strong investors, we are expanding our team to help accelerate our growth and take FusionAuth to the next level.FusionAuth is hiring a Senior Software Engineer to build and extend our Java-based platform, trusted by thousands of organizations and downloaded over 10 million times. You will design and ship complex features end to end, from technical design through release, and apply protocol knowledge (OAuth 2.x, OpenID Connect, SAML) that customers rely on for correct, secure implementations.This is a senior individual contributor role with real influence. You will review code for correctness and architectural fit, mentor Software Engineers on debugging and testing approaches, and identify tech debt before it slows the team down. You will partner directly with Product, DevSuccess, and Support to translate technical tradeoffs into decisions the business can act on.Every feature you ship runs across customer-managed, self-hosted, and dedicated cloud deployments, so backward compatibility and upgrade paths matter on every change. This position reports to the Engineering Manager.Responsibilities:Feature development: Design and build complex features end-to-end, from technical design through release. Write high-quality, secure, well-tested production code.Technical design: Author Technical Design Documents (TDDs) and provide architecture recommendations on designs led by others.Code and design review: Serve as reviewer of record for parts of the codebase. Review for correctness, test quality, and architectural fit.Testing: Design test approaches for complex features, write end-to-end tests for critical paths, and evaluate test quality during code review.Debugging and troubleshooting: Diagnose and fix multithreaded and concurrency issues. Handle complex issues, including on-call rotation for critical customer issues (off-hours support required, though not the norm).Database: Optimize queries using indexes and constraints. Understand ORM tradeoffs and have basic NoSQL familiarity.Security: Apply least-privilege principles and understand timing attacks and encryption basics (PKI vs. symmetric).AI-augmented development: Use LLMs as part of the SDLC, including code review assistance, documentation drafting, and refactoring. Help the team rethink how work gets done with AI in the loop.Technical roadmap: Identify areas of tech debt and propose focus areas for the team.Cross-functional communication: Present designs and tradeoffs to Product, DevSuccess, and Support. Translate technical constraints for non-engineering partners.Technical influence: Influence team decisions through clear reasoning. Support and sometimes lead knowledge-sharing sessions on FusionAuth's architecture.Customer engagement: Join customer calls to discuss specific technical topics and support complex integration questions.Documentation: Write clear, thorough documentation for the features you ship.QualificationsIf you meet most of the required qualifications below but not all of them, apply anyway. Skills transfer, and we'd rather talk to you than miss you over a checklist.RequiredExperience: 8-10 years of professional software development experience, with demonstrated ownership of complex features from design through release.Education: Bachelor's degree in computer science, or demonstrable experience with a broad set of theoretical topics.Java: Advanced Java skills, including threading, concurrency, and performance profiling.Object-oriented design: Strong object-oriented design and implementation skills.Web fundamentals: Solid understanding of the full web stack ( TCP/IP, REST, and related protocols).Database depth: Real working knowledge of relational databases: query optimization, indexing strategy, and schema design beyond ORM abstractions.Testing: Experience designing test approaches for complex features and writing end-to-end tests, not just unit tests.Full-stack range: Comfortable working up and down the stack, including cloud infrastructure, backend services, and JavaScript on the front end.AI tooling: Comfortable using Claude Code, or a comparable AI-assisted development tool, as part of your daily workflow.Work location: FusionAuth is headquartered in the Denver metro area, and we value the collaboration that comes from working together in person. We strongly prefer candidates local to the Denver metro who can be onsite 1-2 days per week. We're open to candidates in other locations who are willing to travel to our office approximately once per quarter.Preferred:Distributed systems: Experience building highly available, high-performance, multi-threaded, API-first applications.Auth protocols: Working knowledge of OAuth 2.x grant types, OIDC protocol depth, and authentication enterprise integration patterns.Kubernetes: Experience writing a basic manifest or Helm chart, with some familiarity with container orchestration in production.CI/CD: Experience writing GitHub Actions workflows or comparable CI/CD pipelines.Quantitative approach: Strong, data-driven approach to solving problems.Learning speed: Quick learner, comfortable mastering new technologies and skills rapidly.Communication style: Holds clear technical opinions while staying open to better evidence or team input.Pragmatism: Appreciates first-principles thinking, but knows when to stop theorizing and start building.Startup adaptability: Adaptable to the pace and ambiguity common in a roughly 50-person startup.$140k - $180k expected base salary/OTE range*Onsite Perks & Campus BenefitsNewly upgraded amenity spaces including a sleek tenant lounge and café with booth seating and collaborative workspaces.Access to a fitness studio, showers, lockers, and secure bike storage.Regularly stocked in-suite kitchen with a variety of snacks and beverages to keep you fueled throughout the day.Onsite café offering chef-driven menus with fresh, locally sourced, organic, and non-GMO options to suit diverse dietary needs. Easy ordering via app.3-acres of green space, including communal parks and picnic areas, connected to miles of jogging, biking, and recreation trails.Yoga in the circle and wellness programs to enhance work-life balance.Dedicated outdoor workspaces and patio gathering areas.Ample on-site parking, easy freeway access, and high-speed fiber internet.Sustainability-minded campus and community initiatives, including support for regenerative agriculture programs.Enjoy a high-tech business environment that inspires creativity and energizes your workday—all just minutes from the heart of Denver and Boulder.*Pursuant to various state laws, we must display the pay range for this job. Since we are willing to hire within a broad spectrum of qualifications, this range is broad. The expected base salary may be adjusted based on individual qualifications, role, level and location.BenefitsComprehensive health insurance including medical, dental, and vision coverage, with the company covering the majority of your medical premiums to keep your costs lowFully employer-paid High Deductible Health Plan (HDHP) option paired with a Health Savings Account (HSA), including employer contributionsBasic life insurance and short- and long-term disability coverage fully paid by the company for essential financial protectionVoluntary life insurance options to provide additional financial protection for you and your loved onesHealthcare and Dependent Care Flexible Spending Accounts (FSAs) to save pre-tax dollars on eligible expenses401(k) plan with company match to help you save for retirementGenerous paid time off (PTO) plus paid company holidays to support work-life balanceEmployee Assistance Program (EAP) offering confidential counseling and support servicesProfessional growth and development opportunities to boost your career journeyEligibility for performance-based bonuses or variable compensation tied to individual, team, or company resultsImportant Details