Senior Backend Engineer: Auth0 CIAM & Migration Lead

Booking Holdings, Inc.; Amsterdam; Hybrid; EUR 90,000 - 130,000; Full time

Benefits offered by this job

Annual paid time off

Hybrid working with flexible remote/

Product discounts – up to 1400 per yr

Job summary

Booking.com is seeking an experienced Backend Engineer to own and evolve partner authentication services. The role spans migrating from legacy Perl to modern Auth0-based authentication, designing robust APIs, and ensuring production reliability across live traffic.

You will work with Java and Perl in a cloud environment, own incident investigations, and contribute to secure, scalable identity platforms. Hybrid work options are available in Amsterdam.

Qualifications

• Backend engineering experience building and operating production services at scale in Java and Perl.
• Hands-on delivery of customer identity and access management (CIAM) for external users (partners, merchants, customers).
• Practical, in-depth experience with Auth0 in production: tenant/configuration, custom logic, token/session design, and operation.
• Experience migrating authentication from incumbent systems to new identity providers on live traffic, with coexistence and rollout strategies.
• Working knowledge of Perl for legacy codebases; ability to read and safely modify code in languages you did not choose.
• Strong grasp of OAuth 2.0, OpenID Connect, JWT, and session management at debugging level.
• Experience running services in a cloud environment with production ownership (deployment, observability, incidents).
• Independent, evidence-led investigation of cross-system production problems.
• Clear written and spoken English and ability to communicate with stakeholders.

Responsibilities

• Build and operate backend services across partner authentication. Design, build, run, and evolve services that broker authentication between Booking.com partner systems and the identity provider.
• Deliver migration workstreams: phased cutovers, coexistence strategies, and rollback plans while live traffic remains.
• Maintain and change the legacy Perl estate to reduce its footprint.
• Configure and extend the identity platform: Auth0 tenant/config, custom auth logic, and token/session design.
• Lead technical investigations for login-path incidents spanning multiple systems.
• Measure changes on real traffic: define metrics, run experiments, and validate migration impact.
• Support the wider PIAM team and its consumers by providing technical guidance and reviews.
• Participate in on-call for services with partner-visible blast radius.

Skills

Backend engineering

Java

Perl

Auth0

CIAM

On-call

Tools

Auth0

Cloud (AWS)

Job description

Booking.com is seeking an experienced Backend Engineer to own and evolve partner authentication services. The role spans migrating from legacy Perl to modern Auth0-based authentication, designing robust APIs, and ensuring production reliability across live traffic.

You will work with Java and Perl in a cloud environment, own incident investigations, and contribute to secure, scalable identity platforms. Hybrid work options are available in Amsterdam.