Building a provider

Adding a bank to Yapilayer means adding a module — never touching the core. The worked example throughout is providers/mock-bank/, the reference connector.

The contract

Three interfaces in providers/provider-sdk (ADR 0004):

public interface BankConnector {
    ProviderDescriptor descriptor();                    // id, name, country, capabilities
    default Optional<AisProviderPort> aisPort() { … }   // present iff AIS declared
    default Optional<PisProviderPort> pisPort() { … }   // present iff PIS declared
}

AisProviderPort covers the consent → authorise → exchange → accounts/balances/transactions flow; PisProviderPort covers payment consent → authorise → submit → status. Two rules make connectors composable:

1. Stateless — all consent/session state arrives through method parameters (ProviderSession); never cache tokens in the connector.
2. Errors stay wrapped — throw ProviderException; bank-specific error details must not leak upward.

Steps

1. Create the module — providers/your-bank/, add one line to settings.gradle.kts, depend on provider-sdk. Connectors need no Spring: the mock connector is plain Java + Jackson over the JDK HTTP client.
2. Implement the descriptor — declare only the capabilities the bank actually supports.
3. Implement the ports — map the bank's API to the domain types (Account, Balance, Transaction, PaymentStatus). If the bank distinguishes API host from customer-facing authorisation host, take both URLs (the mock connector's apiBaseUrl/publicBaseUrl split).
4. Register it — add the connector to ProvidersConfiguration in platform-bootstrap with its configuration properties.
5. Test it — the pattern in ConnectorEndToEndTest: drive the real connector through complete AIS and PIS journeys against the bank's sandbox (or your own simulator).

Documentation expectations

Per PRODUCT_REQUIREMENTS.md §10, each real-bank connector ships with: the developer-portal URL and sandbox registration steps, certificate requirements, OAuth configuration, and known limitations. Put this in the module's README.