Senior Software Engineer (APIs, Auth & Integrations)

About the role

Affinity, an AI-first CRM for private capital, is hiring a Senior Software Engineer for its Open Platform team in its new Barcelona office. You will help shape the technical roadmap and implementation of internal and external API layers, a third-party integration platform and access management systems. The company uses a hub-hybrid model with two days in the office per week.

Key responsibilities

• Own product areas essential to customers and the business, working with engineering, product and design teams.
• Drive technical best practices for APIs, integrations and IAM systems.
• Mentor other engineers and promote operational excellence around reliability, performance and scalability.
• Own and evolve the in-house authentication and authorization platform, including a custom auth server and client libraries.
• Design fine-grained access control systems (RBAC, permissions, policy-based authorization) for a multi-tenant customer base.
• Drive technical decisions on identity protocols such as OAuth2/OIDC, SAML and JWT, and partner with security and platform teams to harden authentication flows.

Required profile

• ~7+ years of software engineering experience, with at least 2+ years as a senior team member delivering end-to-end systems.
• Hands-on experience building or maintaining authentication/authorization systems, ideally with custom auth servers or identity providers.
• Experience with web APIs and backend services using modern OOP practices.
• Helped teams solve high-scale challenges, integrate systems or develop business intelligence platforms.
• Proficiency in English.

Required skills

• Core identity protocols: OAuth2/OIDC, SAML, JWT and session/token lifecycle management.
• Designed or extended RBAC or policy-based permission models.
• Relational databases and troubleshooting across network, application, caching, queuing and storage layers.
• Stack used in the company: Ruby on Rails, PostgreSQL, Redis, TypeScript, React, AWS and Kubernetes (role is more backend-focused).

What we offer

• Comprehensive health insurance for you and your family.
• An annual education budget and a learning and development program.
• A monthly budget for wellness memberships or equipment.