BaaS Integration

As Banking-as-a-Service (BaaS) continues to gain traction, fintech teams are increasingly integrating external providers to deliver core banking functions—account issuing, identity verification (KYC), and transaction monitoring—without building everything in-house. 

But adopting BaaS doesn’t mean giving up architectural control. The key lies in designing lightweight, modular integration layers that allow fintechs to stay nimble, maintain compliance, and swap providers without major rewrites. 

At OceanoBe, we’ve worked with banks and fintechs across Europe to implement modular BaaS adapters, focusing on composability, compliance, and long-term maintainability. 

Why Modular Architecture Matters in BaaS Integrations 

Banking services (such as issuing an IBAN or verifying user identity) are often delegated to BaaS vendors like Solaris, Mambu, Treezor, or local providers depending on geography. However, fintech product teams must be able to: 

Switch providers as contracts or needs evolve 

Extend BaaS functionality with proprietary logic 

Maintain visibility and control over user data and flows 

Avoid vendor lock-in while staying compliant with PSD2, AMLD, GDPR, etc. 

The solution? Modular integration layers that wrap around BaaS APIs with clearly defined responsibilities and interface contracts. 

Core Components of a Modular BaaS Layer 

Let’s break down how to design such a system: 

1. Account Issuing Adapter 

Instead of calling the BaaS account issuing API directly from the core product, build an internal service that: 

• Encapsulates BaaS-specific logic (field mappings, retry handling, SLA tracking) 
• Exposes a uniform interface to the rest of your product (e.g. POST /internal/accounts) 
• Logs all outbound requests and responses for auditability 
• Is stateless and cloud-native for autoscaling 

This makes it easy to support multiple providers or switch providers without rewriting your business logic. 

Bonus: You can also mock this layer in staging to reduce sandbox costs or downtime when the BaaS sandbox is unstable. 

 

2. KYC Module 

KYC/AML processes vary dramatically across providers—some use document scanning, others use video identification, and many combine both with fuzzy matching and sanctions checks. 

A modular KYC integration should: 

Support multiple identity providers via a plug-and-play strategy 

Implement KYC orchestration flows (e.g. retry failed steps, request user re-submission) 

Handle PII storage securely with tokenization or field-level encryption 

Ensure all KYC attempts are logged and traceable for regulators 

The key is to decouple KYC logic from product flows—you don’t want business onboarding to break just because one KYC provider is slow or down. 

3. Transaction Monitoring Hook Layer 

Whether you’re monitoring for fraud, AML patterns, or unusual velocity, you’ll likely integrate third-party monitoring solutions—or build your own rule engine. 

Best practices include: 

Use event-driven architecture: emit standardized events like transaction.initiated or transfer.failed 

Route events to the monitoring layer asynchronously, so your core transaction processing isn’t blocked 

Make monitoring decisions (e.g. hold a transfer) via callback hooks to the transaction engine 

Maintain clear audit logs of rule triggers, decisions, and manual overrides 

This allows your team to iterate on compliance logic independently of core payment logic. 

Design Considerations for Scalability & Compliance 

When building modular integrations, keep the following principles in mind: 

Contract-First Interfaces 

Design internal service contracts (OpenAPI/Swagger) before coding. This ensures each module can be versioned, tested, and scaled independently. 

Observability 

Log all API interactions with correlation IDs. Ensure traceability for regulatory audits, debugging, and SLA tracking. 

Security by Design 

Isolate PII and sensitive data in dedicated modules. Use envelope encryption and comply with GDPR retention policies. 

Provider-Agnostic Design 

Don’t let BaaS-specific structures bleed into your business logic. Use adapters and mapping layers to translate fields cleanly. 

Real-World Impact 

One use cases where this process can be showcased is, for example, in a startup that integrates with a European BaaS platform while retaining optionality for a backup provider. Must-have built-ins: 

A common issuing interface with abstracted payloads 

A KYC flow that could switch between providers depending on customer region 

A transaction rules engine that received standardized events from the payment system and made fraud decisions via API callbacks 

This setup allows the startup to expand into two EU markets with different regulatory profiles while keeping their roadmap agile and their compliance team happy. 

Build Smart, Not Just Fast 

BaaS lets fintechs move faster—but with modular architecture, you can move faster and smarter. 

By designing lightweight layers for account issuing, KYC, and transaction oversight, your team gains: 

Better control over compliance 

Reduced vendor risk 

Easier testing and debugging 

Future-proof integrations that can evolve with the market 

In fintech, agility and compliance don’t have to be trade-offs. With the right architecture, they can reinforce each other.