Senior Engineer (OAuth2) Job Description The Senior Engineer plays a pivotal role in supporting Domain's strategy by driving innovation and ensuring the development of high‑quality software solutions. Leveraging advanced technical skills and deep understanding of software engineering principles, the Senior Engineer architects scalable, efficient applications that align with our strategic goals while guiding and mentoring junior team members to foster continuous improvement and engineering excellence. Role and Mission As part of the Identity & Public Platform squad, you will own Domain’s AuthN and AuthZ services, the Developer Portal, and Public API gateway. You’ll manage OAuth client lifecycles, fine‑grained permissions, self‑service API onboarding, and documentation for external developers while integrating with CoStar Group’s global platform. Technical Excellence and Innovation Build high‑quality, scalable, reliable and performant solutions in collaboration with other engineers and tech leads. Keep abreast of latest trends in technology and software engineering and apply responsible engineering principles. Champion and adopt engineering best practices. Participate in and contribute to cross‑domain technology forums such as Architecture Guild and Tech Leadership Guild. Contribute to system health and tech debt backlog for the services you own. Champion engineering efficiency for your team and services. Collaborate with Lead Engineers and Tech Leads on improving processes and system change. Leadership and Collaboration Mentor junior engineers in solution design and building high‑quality solutions. Build a deep understanding of the product and business domain. Collaborate with Product Managers to ensure solutions align with business and customer needs. Operations Be on‑call and respond to incidents when raised. Continuously find ways to improve process and quality of software to reduce incidents over time. Maintain, update and patch systems as and when required. Responsibilities Bachelor’s Degree in a relevant technical specialization. Strong experience in C# / .NET 8+ and ASP.NET Core for distributed backend services. Strong understanding of OAuth2, OpenID Connect and token lifecycle management (PKCE, federation, refresh tokens, assertion grants). Experience designing software solutions for scale. Experience with high‑traffic customer‑facing services. Experience working with tech leads to optimize engineering practices and processes. Experience with one of the common cloud platforms such as AWS, Azure, and/or GCP. Experience with microservices and event‑driven architectures. Experience with SQL data stores (PostgreSQL, MySQL/Aurora) and NoSQL (DynamoDB, Redis). DevOps practices, CI/CD, and infrastructure‑as‑code. Understanding of shift‑left testing and how to implement it in practice. Experience working in Agile environments. Experience mentoring more junior engineers. Familiar with cloud design patterns. Familiar with modern application security practices (OWASP). Highly regarded additional experience Product/application development experience. Experience or familiarity with Duende IdentityServer. Experience migrating or integrating between identity providers. Experience with asynchronous integration patterns such as SNS/SQS, EventBridge. Experience with API gateway platforms – external developer onboarding, usage metering, and credential management. Experience with fine‑grained authorization systems (AuthZed/SpiceDB, OpenFGA, or similar). TypeScript / Node.js for AWS Lambda and infrastructure‑as‑code (CDK). React / Next.js or other modern web frontend frameworks. AWS (or other cloud platform) certification. CoStar Group is an Equal Employment Opportunity Employer; we maintain a drug‑free workplace and perform pre‑employment substance abuse testing. CoStar is committed to creating a diverse environment and is proud to be an equal opportunity workplace and affirmative action employer. All qualified applicants will receive consideration for employment without regard to race, color, religion, gender, gender identity or expression, sexual orientation, national origin, genetics, disability, age, or veteran status. CoStar is also committed to compliance with all fair employment practices regarding citizenship and immigration status. If you are a qualified individual with a disability or a disabled veteran, you may request a reasonable accommodation if you are unable or limited in your ability to use or access as a result of your disability. You can request reasonable accommodations by calling 1‑855‑840‑1715 or by sending an email to #J-18808-Ljbffr