(調査中)Javaの HttpClient を使用したKeycloakからBearerトークンを取得

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Service;

import java.net.URI;
import java.net.URLEncoder;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.nio.charset.StandardCharsets;
import java.util.Map;
import java.util.stream.Collectors;

@Service
public class KeycloakService {

    public ResponseEntity<String> getToken() {
        String keycloakUrl = "http://your-keycloak-url/auth/realms/your-realm-name/protocol/openid-connect/token";
        String clientId = "your-client-id";
        String clientSecret = "your-client-secret";

        HttpClient httpClient = HttpClient.newHttpClient();

        // リクエストパラメータを準備
        Map<String, String> params = Map.of(
                "grant_type", "client_credentials",
                "client_id", clientId,
                "client_secret", clientSecret
        );

        // URLエンコードされたクエリストリングを作成
        String requestBody = params.entrySet().stream()
                .map(p -> URLEncoder.encode(p.getKey(), StandardCharsets.UTF_8)
                        + "=" + URLEncoder.encode(p.getValue(), StandardCharsets.UTF_8))
                .collect(Collectors.joining("&"));

        // POSTリクエストを作成
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create(keycloakUrl))
                .header("Content-Type", "application/x-www-form-urlencoded")
                .POST(HttpRequest.BodyPublishers.ofString(requestBody))
                .build();

        try {
            // リクエストを送信してレスポンスを取得
            HttpResponse<String> response = httpClient.send(request, HttpResponse.BodyHandlers.ofString());

            // HttpResponseをResponseEntityに変換
            HttpHeaders headers = new HttpHeaders();
            response.headers().map().forEach((key, values) -> headers.put(key, values));

            return new ResponseEntity<>(response.body(), headers, HttpStatus.valueOf(response.statusCode()));
        } catch (Exception e) {
            e.printStackTrace();
            return new ResponseEntity<>(e.getMessage(), HttpStatus.INTERNAL_SERVER_ERROR);
        }
    }
}