Open Banking API Integration

Enterprise-grade API aggregator platform built with Spring Boot, Oracle DB, and Kafka. Handles 10M+ transactions daily with 99.9% uptime, connecting 2000+ European banks in compliance with PSD2 Open Banking Directive.

  • Duration

    12 months+

  • Methodology

    Agile

  • Category

    Fintech

  • Technologies

    • Backend: Java 17, Spring Boot 3.x
    • Database: Oracle 19c, PostgreSQL
    • Messaging: Apache Kafka, RabbitMQ
    • Infrastructure: Docker, Kubernetes, AWS
    • Security: OAuth 2.0, JWT, SSL/TLS
    • Monitoring: Prometheus, Grafana, ELK Stack

  • Project team

    • 8 Senior Java Developers
    • 2 DevOps Engineers
    • 2 QA Specialists
    • 1 Solution Architect
    • 1 Technical PM

Start

Our plan

First, to able to deliver what is a huge scope of work, we needed to draft a plan to make sure of the task's feasibility, whick looked like this:

  • summary

    The product is an enterprise-grade API aggregator (API Hub) built in full compliance with the PSD2 Open Banking Directive. Our unified API platform connects 2000+ European banks, providing fintech startups and enterprises with seamless access to banking data and payment services. The platform handles over 10 million transactions daily with 99.9% uptime, ensuring reliable and secure financial data aggregation across Europe.

  • Objective

    To realize a massive scope of work and deliver a unique standardized API regardless of what API standards are used by each bank.

  • Project Business Tasks

    Guarantee the compliance with all the PSD2 rules and Open Banking principles;
    Create a safe and reliable opportunity for Fintech startups to use the banks' data;
    Ensure banks’ data security.

  • Project Technical Tasks


    Create a single unified API for the banks;
    Deliver real-time access to bank data;
    Provide Strong Customer Authentication (SCA);
    Ensure equal opportunities for all the Account Information Service providers (AISP) and Payment Initiation Service providers (PISP).

What we decided to do

our solution

Smartym Pro development team was to connect 2000+ European banks to an API aggregator - the task was quite straight-forward, yet time-consuming. Basically, the project’s workflow looked like this:

  • 1

    Subject investigation

    Everyone involved in this project had to acquire some specific knowledge before actually starting to work with banks’ APIs. It proved to be a lenghty stage of the development process, especially since the APIs of some banks were 100% custom and didn’t meet any of the common European standards.

  • 2

    Connecting the banks’ APIs
    to the aggregator

    This stage of the workflow was rather routine since the majority of APIs were already standardized and we had instructions that could be applied to most of them. However, as it had been mentioned earlier, there were numerous custom APIs - in those cases, we couldn’t apply the same methods to them. As a result, the estimated labor costs were increased by 30%.

  • 3

    Testing banks
    in the sandbox

    As soon as the connection between a bank’s API and the aggregator was set, the team would move to the testing stage. First of all, the developers used the sandbox, provided by the bank itself. In order to check the operability, such test credentials were used: UTP-code, login, IBAN number, etc. An important note: the data security is ensured by the bank since we enter the credentials on the bank’s page, hence the aggregator is no more than a mediator.

  • 4

    Testing banks
    in the production environment

    The developers sent the bank to a “beta” in order to test it. If everything was alright, the software engineers would just deliver the “sandbox” links to production.

  • 5

    Done

    Once the bank is sent to a “beta”, we deliver it to the client - so that he could test the functionality one more time by himself, using the real credentials. If these stages ended up being successful, the bank would be officially considered ready for Open Banking.

What we faced

challenges

In many ways due to the project scale, it's safe to say that we had a couple of problems to solve:

  • Non-standard APIs

    Our team had to bring more than a thousand of bank APIs to a common standard; some of them were poorly made, others were completely bizarre - not compliant with any of the generally recognized European standards. It was a big challenge for every single member of our software development team, however, it also boosted our motivation, since completing the work in such an environment would always be something to brg about to colleagues.

  • Testing

    At the start of the project, there were few banks, so our testing was manual according to the test-cases our QA specialists had been provided beforehand. However, as time went by, more and more banks needed to be dealt with. Manual testing was no longer an option as one person couldn't test hundreds of APIs in a short period of time. Thus we introduced automated tests, but it was still not enough - the percentage of failed tests was too high, because every bank had its own unique UI, so one automated test for 2000 banks wasn’t the best idea. So we ended up creating semi-automated tests, which were half manual and half automated, tailored to the banks’ specific features. As a result, we were able to process 2000 banks with great success.

result

Successfully connected 2000+ European banks to our unified API platform, achieving 99.9% uptime and processing over 10 million transactions daily. The platform reduced integration time for fintech companies from months to days, enabling rapid deployment of Open Banking solutions.

Implemented comprehensive security measures including OAuth 2.0, JWT authentication, and end-to-end encryption, ensuring full PSD2 compliance. Our automated testing framework reduced manual testing effort by 80% while maintaining 99.5% test coverage across all bank integrations.

The platform has become a cornerstone of the European Open Banking ecosystem, serving as a trusted intermediary for major fintech companies and enabling seamless financial data aggregation across borders.

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