Senior Engineer (OAuth2)

Job Description

CoStar Group (NASDAQ: CSGP) is a leading global provider of commercial and residential real estate information, analytics, and online marketplaces. Included in the S&P 500 Index and the NASDAQ 100, CoStar Group is on a mission to digitize the world’s real estate, empowering all people to discover properties, insights and connections that improve their businesses and lives.

We have been living and breathing the world of real estate information and online marketplaces for over 35 years, giving us the perspective to create truly unique and valuable offerings to our customers. We’ve continually refined, transformed and perfected our approach to our business, creating a language that has become standard in our industry, for our customers, and even our competitors. We continue that effort today and are always working to improve and drive innovation. This is how we deliver for our customers, our employees, and investors. By equipping the brightest minds with the best resources available, we provide an invaluable edge in real estate.

Domain is a leading property technology and services marketplace that is home to one of the largest portfolios of property brands in Australia, including the Domain, Allhomes and Commercial Real Estate (CRE) platforms. In 2025, Domain became part of CoStar Group (NASDAQ: CSGP), a global leader in commercial real estate information, analytics, online marketplaces and +3D digital twin technology. Together, Domain and CoStar Group is dedicated to digitising the world’s real estate, empowering all people to discover properties, insights, and connections that improve their businesses and lives.

The role of Senior Engineer is pivotal in supporting the delivery of our Domain Strategy by driving innovation and ensuring the development of high-quality software solutions. By leveraging advanced technical skills and a deep understanding of software engineering principles, the Senior Engineer contributes to the creation of robust, scalable, and efficient applications that align with our strategic goals. This role involves not only writing and reviewing code but also architecting solutions that meet both current and future business needs, ensuring Software Solutions supports the overall Domain vision.

In addition to technical expertise, the Senior Engineer plays a crucial role in mentoring and guiding junior team members, fostering a culture of continuous improvement and Engineering excellence. By leading by example and providing support, this role helps build a strong, cohesive team capable of tackling complex challenges and delivering high-quality software products. The Senior Engineer also collaborates closely with cross-functional teams, including product management, to ensure that software solutions are aligned with customer value and business needs.

Moreover, the Senior Engineer is instrumental in driving strategic initiatives related to Engineering efficiency and innovation. By staying abreast of the latest industry trends and emerging technologies, this role ensures that our software development practices remain cutting-edge and efficient. The Senior Engineer identifies opportunities to reduce TOIL, improve development workflow, and implement best practices that contribute to the organization's overall strategic objectives. Through proactive problem-solving and strategic thinking, this role supports the company's long-term growth and success, aligning technological advancements with business priorities.

Crew and Squad Mission

The Identity & Public Platform squad owns Domain's AuthN and AuthZ services, as well as the Domain Developer Portal and Public API gateway. We are responsible for ensuring secure, reliable access to Domain's products for both internal and external consumers, managing everything from OAuth client lifecycles and fine-grained permissions to self-service API onboarding and documentation for external developers. As we evolve the Domain technology landscape, our squad plays a pivotal role in the integration with CoStar Group’s global platform. We focus on maintaining the critical-path services that underpin every authenticated interaction at Domain while evolving our architecture to support the global integration and needs of our expanding ecosystem.

The Identity squad is part of Product Platforms Crew - the connective tissue that enables Domain's product teams to focus on what makes them unique. We evolve shared capabilities enabling Domain to move faster with reliable foundations. We are a tech-led crew with a product mindset: our customers are Domain's internal product squads, and our success is measured by their velocity and the reliability of the services we provide. We operate with ruthless focus, co-create with stakeholders, and earn trust through consistent delivery and measurable impact.

Role

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. Use responsible engineering principles to understand when and how to apply those same trends. 
• 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 the System Health and Tech debt backlog for their respectively owned service.
• Champion engineering efficiency for their respective team and services. 
• Collaborate with Lead Engineers and Tech Leads on improving process and system change. 

Leadership and Collaboration

• Mentor more Junior Engineers in Solution design and building high quality solutions. 
• Build a deep understanding of their product and business domain. 
• Collaborate with Product Managers to ensure that solutions aligned 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 specialisation
• 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 optimise engineering practices and processes 
• Experience working 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 (SNS/SQS, EventBridge) integration patterns
• 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