WhoisLookup.cs

class WhoisLookup
{
  private readonly string webApiBaseAddress = "http://api.hackertarget.com/whois/?q=";
  public string HostToLookup { get; private set; }

  public WhoisLookup(string hostToLookup)
  {
    HostToLookup = hostToLookup;
  }

  public async Task<string> GetWhoisInformationsAsync()
  {
    var client = new HttpClient();
    var apiRequestUrl = $"{webApiBaseAddress}{HostToLookup}";

    var getContentAsStringTask = client.GetStringAsync(apiRequestUrl);

    return await getContentAsStringTask;
  }
}