Senior Software Engineer, Security

Job description

About this role

Flex is building the AI-native private bank for business owners . We’re re-architecting the entire financial system for entrepreneurs—from the first dollar a business earns to how that value compounds, moves, and is ultimately spent in real life. Banking, credit, payments, personal finance, and financial operations—rebuilt from the ground up as a single, intelligent system. Flex is the full financial home for ambitious owners. Since launching publicly in September 2023 , Flex has scaled from zero to nine-figure annualized revenue , with a clear path to profitability by late 2026 . We move fast, ship relentlessly, and operate with extreme…

Responsibilities

• Threat model the paths that move money: the ledger and write path, card issuing, payouts, and the stablecoin work. Do it inside design review on anything that touches money, continuously, not as a quarterly exercise.
• Build secure-by-default infrastructure. Infrastructure as Code (IaC) guardrails, CI/CD supply chain integrity, secrets handling, service isolation, and workload IAM.
• Build a just-in-time, least-privilege access system for cloud access that makes engineers faster while narrowing what any one credential can do.
• Own application security across both new and existing systems. Continuously assess the highest-risk parts of what we've already shipped, and build automated checks and secure defaults into the development lifecycle so the same problems stop arriving. Code…
• Build a golden path that keeps sensitive data out of logs, and the tooling that proves it stayed out.

Qualifications and requirements

• Substantial hands-on experience building or securing systems in a fast-moving environment, including a stretch where you were the most senior person doing this work. We care about what you've built, not the year count.
• Real software engineering ability in a language we'd ship (Python, Go, TypeScript, or similar). Not scripting alone.
• Hands-on cloud infrastructure experience: AWS or GCP, Terraform or equivalent IaC, containers, and CI/CD pipelines you've changed, not only used.
• Practical threat modeling on systems with real consequences, and the judgment to know which findings matter.
• Experience with secrets management, workload identity, and service-to-service authorization.
• Flex is building the AI-native private bank for business owners. We’re re-architecting the entire financial system for entrepreneurs—from the first dollar a business earns to how that value compounds, moves, and is ultimately spent in real life. Banking, credit, payments, personal finance, and financial operations—rebuilt from the ground up as a single, intelligent system. Flex is the full financial home for ambitious owners. Since launching publicly in September 2023, Flex has scaled from zero to nine-figure annualized revenue, with a clear path to profitability by late 2026. We move fast, ship relentlessly, and operate with extreme ownership. Our customers are affluent business owners ($3–$200M in revenue)—the backbon