(Senior) Backend Engineer (IAM and Billing)

Details

About Langfuse

Open Source LLM engineering platform that helps teams build useful AI applications via tracing, evaluation, and prompt management. Langfuse is now part of ClickHouse. The company is engineering-heavy with teams in Berlin and San Francisco and is hiring for engineering in EU timezones. The team expects one week per month in the Berlin office and works hybrid.

Role summary

You will own core platform systems for authentication, authorization, and billing used across Langfuse Cloud and self-hosted deployments. This includes designing the identity and access model, building usage-based billing and metering pipelines, and creating shared platform APIs that product teams consume. The role has high-impact scope: authentication, authorization, and billing are foundational systems that affect every product surface.

Responsibilities

• Build and evolve authentication systems (SSO/SAML, OAuth, API key management, session handling).
• Design and implement fine-grained authorization (RBAC and eventually ABAC), permission models, and scoped access controls for enterprise customers.
• Own usage-based billing infrastructure: accurate metering of trace events at scale, payment provider integration, plan management, entitlements, and invoicing.
• Create clean, well-documented internal platform APIs and abstractions for auth and billing.
• Ensure auth and billing work for both Langfuse Cloud and self-hosted deployments, integrating with enterprise identity stacks (LDAP, OIDC, SAML).
• Build for enterprise adoption concerns: audit logging, compliance, multi-tenant isolation, and complex pricing models.
• Design systems with attention to security, edge cases, and failure modes.

Requirements

• Strong backend engineering experience building secure, reliable platform systems.
• Experience building authentication and authorization systems (SSO/SAML, OAuth, RBAC, API key management).
• Familiarity with billing or payments infrastructure, usage-based metering, and payment provider integrations (Stripe or similar).
• Careful thinking about security, edge cases, and failure modes in multi-tenant environments.
• Strong opinions about API design and system boundaries; ability to ship shared infrastructure safely.
• Comfortable reading and writing TypeScript (backend) and SQL.
• Interest in open source software and empathy for self-hosted operators integrating with their own identity stacks.
• Thrives in a small, accountable team where individual output is visible.
• CS or quantitative degree preferred.

Bonus points

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

Process

The company can complete a full hiring process to offer in less than 7 days.

Tech stack

• TypeScript monorepo (backend in TypeScript).
• Frontend: Next.js.
• Background workers: Express.
• Transactional DB: PostgreSQL.
• Tracing / analytics: ClickHouse.
• File storage: S3.
• Queues and caching: Redis.

How we ship

• Engineers take ownership, propose RFCs, and ship features.
• Code reviews are mentorship-focused and new joiners get PR reviews to learn the codebase.
• The team follows a maker schedule with two recurring meetings per week (short Monday check-in and a Friday demo). They use AI tooling in workflows and encourage experimentation.

Why Langfuse (now part of ClickHouse)

• Open-source devtools company focused on AI tooling and observability for LLM-based applications.
• High-impact, visible work with open-source visibility and direct product ownership.
• Opportunity to work closely with ClickHouse and learn from a world-class infrastructure team.
• Fast shipping cadence and close customer feedback loops.