Open Finance: five architecture decisions before you expose your first API
Regulatory compliance is only the starting point. Whether your open APIs generate revenue or technical debt depends on five decisions best made before the first endpoint is written.
Open finance has moved from an innovation talking point to a regulatory and commercial agenda. In Colombia, Decree 1297 of 2022 set the framework for open finance; across the region, Brazil and Mexico have been building their own schemes for years. For a bank, fintech or insurer, the question is no longer whether to expose APIs, but how to do it without putting the core at risk or piling up technical debt.
In the projects we support, success is decided before the first endpoint is written. These are the five decisions we recommend making first.
1. Treat APIs as a product, not a project
An open API has external consumers, contracts and stability expectations. That calls for a catalog, versioning and a lifecycle, like any other product.
- Contract first: design with OpenAPI (and AsyncAPI for events) and validate the contract before implementing.
- Explicit versioning and a published deprecation policy for third parties.
- An API gateway as the single point for authentication, quotas, routing and per-consumer metrics.
2. Security and consent as first-class services
In open finance, customer consent is the central asset. It can't be a column in a table: it needs its own service, with full traceability of who authorized what, to whom, for what purpose and until when.
- OAuth 2.0 with high-security profiles such as FAPI from the OpenID Foundation, designed for financial APIs.
- mTLS between participants and tokens with minimal scope.
- Immediate consent revocation, propagated to every system that consumes that data.
3. Protect the core: decouple with events
The most expensive mistake is wiring open APIs straight into core banking. Third-party traffic is unpredictable, and the core wasn't built for it.
The pattern that works best combines change data capture (CDC) from the core, an event bus such as Kafka, and an anti-corruption layer that translates the legacy model into the API's canonical model. Reads are served from optimized views, and the core only receives the operations that truly belong to it.
Rule of thumb: no third-party call should reach the core without passing through a layer that can throttle, cache or queue it.
4. Data governance by design
Exposing data means knowing exactly what it is, where it comes from and how good it is when it leaves. A data catalog, lineage and automated quality rules keep an internal error from becoming an incident with a partner.
It's also the moment to apply data minimization: each API returns only what the consent covers, in line with data protection law and sector regulation.
5. Design operations before launch
An open API in production is a service commitment to third parties. Before going live, define:
- Service level objectives (SLOs) for availability and latency per API.
- End-to-end observability, with traces that follow each request from the gateway to the source system.
- A sandbox with synthetic data so partners can integrate without touching production.
- Per-consumer rate limits and a clear support and incident process.
Where to start
We recommend a short assessment that measures current maturity across these five dimensions and prioritizes a roadmap. In our work with financial institutions, that early clarity is what makes it possible to speed up time-to-market for new products without trading away compliance or scalability.