Senior Backend Engineer (IAM and Billing)

Details

About Langfuse

Langfuse is an open-source LLM engineering platform that helps teams build useful AI applications through tracing, evaluation, and prompt management. Langfuse is now part of ClickHouse and serves more than 2,000 customers, including 19 of the Fortune 50, with more than 26 million monthly SDK downloads and over 6 million Docker pulls.

The company has an engineering-heavy team in Berlin and San Francisco and also hires engineers across EU time zones. The role is expected to spend one week per month in the Berlin office.

Responsibilities

• Own and evolve authentication and identity systems, including SSO/SAML, OAuth, API key management, and session handling.
• Design fine-grained authorization models for organizations, projects, roles, and scoped access controls using RBAC and eventually ABAC.
• Build usage-based billing infrastructure that accurately meters trace events at scale, integrates with payment providers, and generates invoices.
• Handle plan management, entitlements, and self-service upgrade flows.
• Create clean, well-documented internal APIs and abstractions for authentication and billing.
• Support self-hosted deployments and integrations with enterprise identity providers and identity stacks, including LDAP, OIDC, and SAML.
• Scale IAM and billing infrastructure for enterprise adoption, including audit logging, compliance requirements, multi-tenant isolation, and complex pricing models.
• Own critical shared components end to end, from design through production.
• Propose solutions through RFCs, ship independently, and manage delivery through Linear.

Requirements

• Strong backend engineering experience designing secure and reliable platform systems.
• Experience building authentication and authorization systems, including SSO/SAML, OAuth, RBAC, and API key management.
• Familiarity with billing or payments infrastructure, including usage-based metering, payment provider integrations such as Stripe, and entitlements.
• Careful consideration of security, edge cases, failure modes, and multi-tenant environments.
• Strong opinions about API design, system boundaries, and safely shipping shared infrastructure.
• Comfortable reading and writing TypeScript and SQL.
• Interest in open-source software and empathy for self-hosted operators integrating with their own identity stacks.
• Ability to thrive in a small, accountable team where work is visible and impactful.
• A computer science or quantitative degree is preferred.

Bonus Qualifications

• Experience building multi-tenant SaaS platforms with enterprise identity requirements.
• Background in usage-based billing systems or fintech infrastructure.
• Familiarity with SOC 2 and GDPR as they relate to authentication and data access.
• Former founder.

Tech Stack

The company runs a TypeScript monorepo with Next.js on the frontend, Express workers for background jobs, PostgreSQL for transactional data, ClickHouse for tracing at scale, S3 for file storage, and Redis for queues and caching.

Engineering Culture

The team emphasizes ownership, RFC-driven development, collaboration, maker schedules, mentorship through code reviews, and experimentation with AI tooling. There are recurring Monday priority check-ins and Friday demo sessions. The full hiring process can be completed in less than seven days through the offer-letter stage.

Benefits

• Salary of €90,000–€160,000 per year.
• Equity offered.