Gist meant to test a payment mandate creation with truelayer-signing-java7 library

AccessToken.java

package com.truelayer.payments_jdk7.entities;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;

public class AccessToken {
    private final String accessToken;

    private final int expiresIn;

    private final String scope;

    private final String tokenType;

    @JsonCreator(mode = JsonCreator.Mode.PROPERTIES)
    public AccessToken(@JsonProperty("access_token") String accessToken, @JsonProperty("expires_in") int expiresIn, @JsonProperty("scopes") String scope, @JsonProperty("token_type") String tokenType) {
        this.accessToken = accessToken;
        this.expiresIn = expiresIn;
        this.scope = scope;
        this.tokenType = tokenType;
    }

    public String getAccessToken() {
        return accessToken;
    }

    public int getExpiresIn() {
        return expiresIn;
    }

    public String getScope() {
        return scope;
    }

    public String getTokenType() {
        return tokenType;
    }
}

CreateMandateResponse.java

package com.truelayer.payments_jdk7.entities;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;

public class CreateMandateResponse {
    private final String id;

    private final String resourceToken;

    @JsonCreator(mode = JsonCreator.Mode.PROPERTIES)
    public CreateMandateResponse(@JsonProperty("id") String id, @JsonProperty("resource_token") String resourceToken) {
        this.id = id;
        this.resourceToken = resourceToken;
    }

    public String getId() {
        return id;
    }

    public String getResourceToken() {
        return resourceToken;
    }
}

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.truelayer.payments-jdk7</groupId>
  <artifactId>payments-jdk7</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>payments-jdk7</name>
  <url>https://maven.apache.org</url>

  <properties>
    <maven.compiler.target>1.7</maven.compiler.target>
    <maven.compiler.source>1.7</maven.compiler.source>
  </properties>

  <repositories>
    <repository>
      <id>maven-central</id>
      <url>	https://repo1.maven.org/maven2/</url>
    </repository>
  </repositories>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.13.2</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.datatype</groupId>
      <artifactId>jackson-datatype-jdk7</artifactId>
      <version>2.6.7</version>
    </dependency>
    <dependency>
      <groupId>com.truelayer</groupId>
      <artifactId>truelayer-signing-java7</artifactId>
      <version>0.0.4</version>
      <type>jar</type>
    </dependency>
    <dependency>
      <groupId>com.squareup.okhttp3</groupId>
      <artifactId>okhttp</artifactId>
      <version>3.12.0</version>
    </dependency>
  </dependencies>
</project>

TruelayerClient.java

package com.truelayer.payments_jdk7;

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.truelayer.payments_jdk7.entities.AccessToken;
import com.truelayer.payments_jdk7.entities.CreateMandateResponse;
import com.truelayer.signing.Signer;
import okhttp3.*;

import java.io.IOException;
import java.util.UUID;

public class TrueLayerClient {

    public static final String HEADER_IDEMPOTENCY_KEY = "Idempotency-Key";
    public static final String HEADER_TL_SIGNATURE = "Tl-Signature";
    public static final String HEADER_AUTHORIZATION = "Authorization";
    public static String AUTH_ENDPOINT = "https://auth.truelayer-sandbox.com";
    public static String PAYMENTS_API_ENDPOINT = "https://api.truelayer-sandbox.com";

    private static OkHttpClient httpClient;
    private static ObjectMapper objectMapper;

    static {
        httpClient = new OkHttpClient();

        objectMapper = new ObjectMapper();
        // do not include null fields in JSON
        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        // do not fail in case of unknown properties returned JSON payloads
        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    }

    public static CreateMandateResponse createMandate() throws IOException {

        RequestBody formData = new FormBody.Builder()
                .add("client_id", System.getenv("TL_CLIENT_ID"))
                .add("client_secret", System.getenv("TL_CLIENT_SECRET"))
                .add("grant_type", "client_credentials")
                .add("scopes", "payments")
                .build();

        Request getAccessTokenReq = new Request.Builder()
                .url(AUTH_ENDPOINT + "/connect/token")
                .post(formData)
                .build();

        ResponseBody getTokeResponseBody = httpClient.newCall(getAccessTokenReq).execute().body();

        AccessToken token = objectMapper.readValue(getTokeResponseBody.string(), AccessToken.class);

        if(token == null || token.getAccessToken().length()==0){
            throw new RuntimeException("Unable to get an access token. Aborting");
        }

        String createMandateJsonReq = "{\"mandate\":" +
                "{\"type\":\"sweeping\",\"provider_selection\":{\"type\":\"preselected\",\"provider_id\":\"ob-natwest-vrp-sandbox\"," +
                "\"remitter\":{\"account_holder_name\":\"SydneyBeard\",\"account_identifier\":{\"type\":\"sort_code_account_number\",\"sort_code\":\"500000\",\"account_number\":\"12345601\"}}}," +
                "\"beneficiary\":{\"type\":\"external_account\",\"account_holder_name\":\"Andrea\",\"account_identifier\":{\"type\":\"sort_code_account_number\",\"sort_code\":\"040662\",\"account_number\":\"00003924\"}}}," +
                "\"currency\":\"GBP\",\"user\":{\"id\":\""+UUID.randomUUID()+"\",\"name\":\"Bob Marley\",\"email\":\"bob@truelayer.com\",\"phone\":\"+39333122334\"}," +
                "\"constraints\":{\"valid_from\":\"2022-08-31T00:00:00.000Z\",\"valid_to\":\"2025-01-01T00:00:00.000Z\",\"maximum_individual_amount\":1000,\"periodic_limits\":{\"month\":{\"maximum_amount\":10000,\"period_alignment\":\"calendar\"}}}}";

        String kid = System.getenv("TL_SIGNING_KEY_ID");
        if (kid == null) throw new RuntimeException("Missing env var KID");

        String privateKeyPem = System.getenv("TL_SIGNING_PRIVATE_KEY");
        if (privateKeyPem == null) throw new RuntimeException("Missing env var PRIVATE_KEY");

        String idempotencyKey = UUID.randomUUID().toString();
        String tlSignature = Signer.from(kid, privateKeyPem)
                .header(HEADER_IDEMPOTENCY_KEY, idempotencyKey)
                .method("post")
                .path("/mandates")
                .body(createMandateJsonReq)
                .sign();

        RequestBody createMandateJsonBody = RequestBody.create(MediaType.parse("application/json; charset=utf-8"),
                createMandateJsonReq);

        Request createMandateReq = new Request.Builder()
                .header(HEADER_AUTHORIZATION, "Bearer "+token.getAccessToken())
                .header(HEADER_TL_SIGNATURE, tlSignature)
                .header(HEADER_IDEMPOTENCY_KEY, idempotencyKey)
                .url(PAYMENTS_API_ENDPOINT + "/mandates")
                .post(createMandateJsonBody)
                .build();

        ResponseBody createMandateResponseBody = httpClient.newCall(createMandateReq).execute().body();

        CreateMandateResponse createMandateResponse = objectMapper.readValue(createMandateResponseBody.string(), CreateMandateResponse.class);

        return createMandateResponse;
    }
}

TruelayerClientTest.java

package com.truelayer.payments_jdk7;

import com.truelayer.payments_jdk7.entities.CreateMandateResponse;
import org.junit.*;

import java.io.IOException;


public class TrueLayerClientTest
{
    @Test
    public void testTlClient() throws IOException {
        CreateMandateResponse createMandateResponse = TrueLayerClient.createMandate();

        Assert.assertNotNull(createMandateResponse.getId());
        Assert.assertNotNull(createMandateResponse.getResourceToken());

        System.out.println("created mandate with id "+createMandateResponse.getId());
    }
}