Freelance Java Back End Developer Jobs in Toronto, ON

Citi is looking for a Principal Backend Engineer to take strategic ownership of the backend architecture powering a digital experience platform that serves hundreds of thousands of clients and processes millions of web requests every day. In this senior individual contributor role, you will shape the technical direction of a large-scale, federated system - designing and building the high-performance backend services that connect internal and external users to an integrated digital experience. You will operate at the intersection of hands-on engineering and architectural leadership, influencing technology decisions that have real, measurable impact at enterprise scale.

Responsibilities Design and build high-performance, fault-tolerant backend services and APIs in Java that power authentication, authorization, content routing, and data integration at enterprise scale. Define and evolve the backend architecture of a large-scale federated platform, ensuring systems are scalable, secure, maintainable, and resilient. Implement end-to-end security controls across backend components, including single sign-on, centralized entitlements, and adherence to cyber defense standards.

Engineer backend systems for optimal performance by applying caching strategies, asynchronous processing, and efficient data access patterns. Architect integration solutions that connect diverse content provider applications into a unified platform via HTTPS-based interfaces. Mentor senior engineers through in-depth code reviews and practical guidance on design patterns, testing practices, and operational excellence.

Lead root cause analysis and resolution of complex production incidents, acting as the go-to technical authority for critical backend services. Collaborate with product, front-end, infrastructure, and security teams to translate business requirements into reliable, end-to-end technical solutions. Required qualifications & skills 6 to 10 years of backend software development experience, including significant time architecting and leading complex, large-scale enterprise platforms.

Expert-level proficiency in Java, with hands-on experience across associated frameworks and the ability to produce production-grade code at pace. Deep practical knowledge of distributed systems, microservices architecture, and RESTful API design. Demonstrated ability to implement identity and access management solutions, including OAuth2 and OpenID Connect protocols and fine-grained authorization models.

Solid experience with cloud-native development on GCP and AWS, including containerization with Docker and orchestration with Kubernetes. Confident working across both relational and NoSQL database technologies and selecting the right approach for the problem at hand. Bachelor's degree in a relevant field or equivalent practical experience.

Beneficial skills & qualifications Hands-on experience with Unix environments, Oracle databases, or distributed caching solutions used in high-throughput systems. Exposure to AI tooling or applied machine learning within backend engineering contexts. Working knowledge of front-end integration practices, including ReactJS, Content Security Policy, corporate design system adoption, or accessibility compliance standards.

Preferred Master's degree in computer science, software engineering, or a related discipline. What we offer At Citi, you will work on technology that operates at genuine global scale - shaping systems that millions of people rely on every day. This role offers the opportunity to lead with technical authority, grow your career in a performance-driven environment, and contribute to a platform where engineering decisions carry real weight.

Hybrid working model with 3 days in the office and 2 days working remotely, giving you structure and flexibility. Strategic ownership and influence over architectural decisions that affect a platform serving hundreds of thousands of clients. Access to learning and development resources that support continued technical growth at a senior level.

Collaboration with cross-functional teams across engineering, product, infrastructure, and security on a global scale. Wellbeing support and financial benefits designed to provide long-term value for you and your family. A platform and culture that rewards engineering excellence, clear thinking, and delivery ownership.

Build the backend architecture that powers Citi's digital experience for millions of users - apply today and bring your engineering leadership to a platform that operates at true global scale. This job description provides a high-level review of the types of work performed. Other job-related duties may be assigned as required.

------------------------------------------------------ Job Family Group: Technology ------------------------------------------------------ Job Family: Applications Development ------------------------------------------------------ Time Type: Full time ------------------------------------------------------ Primary Location Full Time Salary Range: $120,800.00 - $170,800.00 ------------------------------------------------------ Most Relevant Skills Please see the requirements listed above. ------------------------------------------------------ Other Relevant Skills For complementary skills, please see above and/or contact the recruiter. ------------------------------------------------------ Automated Processing and AI We use automated processing, including artificial intelligence, for our legitimate business interests (or our reasonable and appropriate business purposes) to identify and align the candidate's skills and abilities with a specific job opening

Additionally, if you so choose, or consent, we can match your skills and abilities to other suitable roles at Citi. Importantly, all our hiring processes and decisions, including determining your suitability for a role, are conducted, checked, and decided by individuals. Our automated processing and AI do not involve relying on automatic or autonomous decision-making.

Please refer to any Jurisdictional Considerations, with specific provisions for your country (where relevant) for further details. ------------------------------------------------------ This job opening is for an existing job vacancy. ------------------------------------------------------ Citi is an equal opportunity employer, and qualified candidates will receive consideration without regard to their race, color, religion, sex, sexual orientation, gender identity, national origin, disability, status as a protected veteran, or any other characteristic protected by law.

If you are a person with a disability and need a reasonable accommodation to use our search tools and/or apply for a career opportunity review Accessibility at Citi. View Citi's EEO Policy Statement and the Know Your Rights poster.