Senior Software Engineer, Backend (Consumer Authentication Platform)

At Affirm, we exist for the moments that matter—giving people a clear, predictable way to pay over time, with no hidden fees, no surprises, and no tradeoffs on what matters most. The Consumer Authentication Platform team is looking for a passionate Senior Software Engineer to help build the secure, reliable, and seamless authentication experiences that connect millions of consumers with Affirm’s financial products. Authentication is the front door to Affirm. Our systems power critical consumer journeys (including sign-up, sign-in, account recovery, checkout authentication, step-up challenges, session management, and connected merchant experiences) across thousands of merchants and multiple countries. We build foundational capabilities such as authentication factors, identity federation, session and authorization services, and risk-based authentication that protect consumers while minimizing unnecessary friction. We work closely with Product, Security, Fraud, Identity, Analytics, Compliance, Data Science, and a wide range of engineering teams to both leverage existing systems and build new systems. This role requires a high level of technical capability, strong cross-functional communication, and a creative mindset. Our work needs to be secure, reliable, correct, scalable, and extensible. Our job is to build an authentication platform that balances security, regulatory requirements, fraud prevention, customer experience, and business growth. As a senior engineer, you will lead significant technical initiatives, influence the architecture and evolution of the platform, and help the team deliver secure authentication capabilities that can be reused across products, merchants, and geographies. What You’ll Do You will own the technical design and delivery of significant authentication platform capabilities, leading projects from early requirements and architecture through implementation, rollout, and ongoing operation. You will build secure, highly available systems that support consumer sign-in, authentication factors, account recovery, step-up authentication, session management, authorization, and identity federation. You will support your peers and stakeholders in the product development lifecycle by collaborating with product management, Security, Fraud, Compliance, design, and analytics; participating in ideation; articulating technical constraints; and partnering on decisions that properly consider risks and trade-offs. You will translate security, regulatory, fraud, and customer-experience requirements into pragmatic technical designs that appropriately balance risk, friction, complexity, and delivery speed. You will proactively identify project, process, technology, security, reliability, or business issues, advocate for them, and lead in solving them. You will support the operations and availability of your team’s artifacts by creating and monitoring metrics, escalating when needed, and supporting “keep the lights on,” and on-call efforts. You will foster a culture of quality, security, and ownership on your team by setting or improving code review and design standards and advocating for them beyond your team through your writing and tech talks. You will help develop talent on your team by providing feedback and guidance, mentoring other engineers through design reviews and hands-on collaboration, and leading by example. You will clearly communicate technical decisions, constraints, risks, and trade-offs to engineering and non-engineering audiences through design documents, reviews, and technical discussions. You will lead the investigation and resolution of complex production issues and identify systemic improvements that prevent recurrence. What We Look For You have 4+ years of experience designing, developing, and launching backend systems at scale using languages like Python, Kotlin, Java, or another comparable modern programming language. You have a track record of developing hi