How can I get the data of the domain users using a service account?

I am developing a corporate application in which we use the People API Directory APi, however, I always need to auto-check from a specific user, since I cannot receive data using a service account. How can I get the data of the domain users using a service account?

I used this code for connection google API.

public class DirectoryService {
@Value("${service.account.email}")
private String SERVICE_ACCOUNT_EMAIL;
@Value("${service.account.pk.file.path}")
private String SERVICE_ACCOUNT_PKCS12_FILE_PATH;

public Directory getDirectoryService(String userEmail){
    HttpTransport httpTransport = new NetHttpTransport();
    JacksonFactory jsonFactory = new JacksonFactory();
    Directory service = null;
    try {
        GoogleCredential credential = new GoogleCredential.Builder()
                .setTransport(httpTransport)
                .setJsonFactory(jsonFactory)
                .setServiceAccountId(SERVICE_ACCOUNT_EMAIL)
                .setServiceAccountScopes(Collections.singleton(DirectoryScopes.ADMIN_DIRECTORY_USER_READONLY))
                .setServiceAccountUser(userEmail)
                .setServiceAccountPrivateKeyFromP12File(
                        new java.io.File(SERVICE_ACCOUNT_PKCS12_FILE_PATH))
                .build();
        service = new Directory.Builder(httpTransport, jsonFactory, null)
                .setHttpRequestInitializer(credential).build();
    } catch (GeneralSecurityException e){
        log.error("Responding \"GeneralSecurityException in Google API.\" in method getDirectoryService().");
        throw new BadRequestException("GeneralSecurityException in Google API.");
    }catch (IOException e){
        log.error("Responding \"Not connection with Google API.\" in method getDirectoryService().");
        throw new BadRequestException("Not connection with Google API.");
    }

    return service;
}

}

        Directory directory = directoryService.getDirectoryService(email);
        Users response = directory.users().list()
                .setDomain("domain.com")
                .setViewType("domain_public")
                .setMaxResults(500)
                .execute();