Java SDK for YTS

Yolt Technology Services (YTS) is a service that provides access to PSD2 APIs of European banks through a single easy to use API enabling use cases like personal financial management, credit scoring, one-off payments, recurring payments, debt collection, instant lending and others.

Read the docs at https://developer.yolt.com/docs.

This Java SDK is a personal project that further simplifies connecting to YTS API. It currently covers AIS. PIS is in progress.

Setting up the SDK

The SDK needs the following information to be able to work with YTS API.

• The base URL of the YTS API, either for the sandbox or production
• The TLS client certificate used to set up an mTLS connection with YTS
• The signing key used to sign token requests

Below is an example of how the YTS SDK can be set up.

// Http client settings
HttpClientConfig httpClientConfig = new HttpClientConfig.Builder("https://api.sandbox.yolt.io")
    .setKeyStore("classpath/to/keystore.pfx", "keystore-pw")
    .setTimeouts(2000, 2000)
    .setLogRequestsResponses(true) // Logs full request / response body and headers
    .build();

// Signing settings
AccessTokenConfig signingConfig = new AccessTokenConfig(
"classpath/to/keystore.pfx",
"keystore-pw",
"signing-key-alias",
"5cd24c9c-7bc0-42fb-aa3d-135bb2361481");

YTS yts = new YTS(appProperties.getClientId(), signingConfig, httpClientConfig);

The YTS class is the single point of entry for all API calls.

Request and response logging

Http calls to YTS are made with Spring WebClient that is configured with Jetty Http Client. Clients can enable request and response logging by setting HttpClientConfig.logRequestsResponses to true.

This JDK uses Jetty HTTP client under the surface. Jetty is an easy to configure HTTP client that allows logging of full request and response body and headers, which helps when debugging potential issues.

Token fetching

The SDK takes care of fetching tokens internally, so clients don't have to request and track access tokens when using this SDK. The default strategy the SDK uses for fetching access tokens from YTS is SlightlyLazyAccessTokenStrategy. This strategy loads a token whenever there is no existing token, or the existing token is more than 9 minutes old. It is slightly lazy in the sense that it will only get a new token when a client makes a request.

A more elegant implementation of the AccessTokenStrategy could fetch a token in a background thread. However, implementers must make sure that such a process is robust and can recover from potential problems such as downtime or HTTP errors.

Scraping and embedded flow

Embedded flow where the user provides credentials via the client app frontend is currently not yet supported in this SDK. This doesn't mean there are no forms at all. For banks like Credit Agricole, Banque Populaire and Caisse d'Epargne YTS implemented a region selection form. These are supported by the SelectField class, so these banks are supported via the SDK.