Add oauth2 client

lib/src/main/java/com/tribufu/sdk/TribufuClient.java

@@ -0,0 +1,39 @@
+// Copyright (c) Tribufu. All Rights Reserved.
+
+package com.tribufu.sdk;
+
+import java.net.http.HttpClient;
+import java.util.HashMap;
+import java.util.Map;
+
+public class TribufuClient {
+    public static final String VERSION = "0.0.0";
+
+    private final long id;
+    private final String secret;
+    private final HttpClient http;
+    private Map<String, String> defaultHeaders;
+
+    public TribufuClient(long id, String secret) {
+        this.id = id;
+        this.secret = secret;
+
+        String targetTriple = "Java";
+        String userAgent = String.format("Tribufu/%s (+https://api.tribufu.com; %s)", VERSION, targetTriple);
+
+        Map<String, String> headers = new HashMap<>();
+        headers.put("User-Agent", userAgent);
+        headers.put("X-Tribufu-Language", "java");
+        headers.put("X-Tribufu-Version", VERSION);
+
+        this.defaultHeaders = headers;
+
+        this.http = HttpClient.newBuilder()
+                .version(HttpClient.Version.HTTP_2)
+                .build();
+    }
+
+    public long getId() {
+        return this.id;
+    }
+}

lib/src/test/java/com/tribufu/sdk/TribufuClientTest.java

@@ -0,0 +1,14 @@
+// Copyright (c) TribuFu. All Rights Reserved
+
+package com.tribufu.sdk;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class TribufuClientTest {
+    @Test
+    void clientGetId() {
+        TribufuClient client = new TribufuClient(0, "client_secret");
+        assertEquals(0, client.getId());
+    }
+}