json to httpcontent c#

// ...

string payload = JsonConvert.SerializeObject(new
{
    agent = new
    {
        name    = "Agent Name",
        version = 1,
    },

    username = "username",
    password = "password",
    token    = "xxxxx",
});

var client = new HttpClient();
var content = new StringContent(payload, Encoding.UTF8, "application/json");

HttpResponseMessage response = await client.PostAsync(uri, content);

// ...