How to POST String Values with .NET HttpClient?

<code class="language-csharp">[ActionName("exist")]
[HttpPost]
public bool CheckIfUserExist([FromBody] string login)
{
    return _membershipProvider.CheckIfExist(login);
}</code>

<code class="language-csharp">using System;
using System.Net.Http;
using System.Threading.Tasks;

class Program
{
    static async Task Main(string[] args)
    {
        await MainAsync();
        Console.ReadKey(); // Keep console window open until a key is pressed
    }

    static async Task MainAsync()
    {
        using (var client = new HttpClient())
        {
            client.BaseAddress = new Uri("http://localhost:6740");
            var content = new StringContent("login", System.Text.Encoding.UTF8, "application/x-www-form-urlencoded");
            var response = await client.PostAsync("/api/Membership/exists", content);
            string responseContent = await response.Content.ReadAsStringAsync();
            Console.WriteLine(responseContent);
        }
    }
}</code>