Senior Backend Engineer — Authentication & Security Platform (Digital Bank)

About Abbeal

Abbeal is an international IT consulting firm (France, Japan, Canada) placing senior engineers on high-impact product teams. Through Abbeal, join the Authentication & Authorization platform of an FSA-regulated digital bank launching in Japan.

The Context

We support an FSA-regulated digital bank launching its platform in Japan. You will join the team building the Authentication & Authorization foundation: OAuth 2.0/OIDC login, token lifecycle and identity management across four banking channels (officer dashboards, customer apps, BaaS APIs, third-party integrations). The team is distributed across Japan, Vietnam and India; the role is anchored on Tokyo with a remote-friendly setup. English is the working language - Japanese is not required.

What You Will Build

• Token lifecycle - DPoP-bound access tokens, silent refresh, session management
• Passkey / FIDO2 - WebAuthn registration and login flows, step-up authentication
• mTLS integrations - certificate-based service-to-service auth with external financial platforms
• Shared security library - Spring Boot starter providing standardized auth filters
• Integration testing - Karate-based suites covering all auth flows at scale
• Monitoring - auth event observability, anomaly detection, audit trail completeness

What We Are Looking For

• 10+ years in server-side backend engineering, including 5-7 years in Kotlin or Java + Spring Boot
• Spring Security (filter chains, OAuth2 Resource Server) and strong OAuth 2.0 / OIDC knowledge
• At least one of DPoP, mTLS, PKCE, FIDO2 / WebAuthn - plus JWT (claims, JWKS, key rotation)
• Redis (sessions, distributed locking, caching) and PostgreSQL (schema design, migrations)
• AWS (ECS/Fargate, Secrets Manager) and Terraform or equivalent IaC
• Strong understanding of the OWASP Top 10 and secure web application development
• Professional English (working language); Japanese not required

Nice to Have

• Authlete; FAPI 2.0 Security Profile; Microsoft Entra ID; Cloudflare / Akamai (mTLS termination, WAF)
• Fintech / regulated banking background (FSA, maker-checker, audit logging); Japanese ability

Why This Role

A real FSA-supervised bank - cutting-edge security standards (FAPI 2.0, DPoP, WebAuthn/FIDO2), high ownership of entire authentication channels, global collaboration on a greenfield platform.

Compensation and Setup

Permanent role, anchored on Tokyo, distributed team, remote-friendly. Indicative range ¥8M-¥17M/year depending on experience. Hired and supported by Abbeal (visa sponsorship + Mobbeal expat support); relocation support possible depending on profile.