Send JSON via POST in C# and Receive the JSON returned?

I found myself using the HttpClient library to query RESTful APIs as the code is very straightforward and fully async'ed. To send this JSON payload:

{  "agent": {                                 "name": "Agent Name",                    "version": 1                                                            },  "username": "Username",                                     "password": "User Password",  "token": "xxxxxx"}

With two classes representing the JSON structure you posted that may look like this:

public class Credentials{    public Agent Agent { get; set; }        public string Username { get; set; }        public string Password { get; set; }        public string Token { get; set; }}public class Agent{    public string Name { get; set; }        public int Version { get; set; }}

You could have a method like this, which would do your POST request:

var payload = new Credentials {     Agent = new Agent {         Name = "Agent Name",        Version = 1     },    Username = "Username",    Password = "User Password",    Token = "xxxxx"};// Serialize our concrete class into a JSON Stringvar stringPayload = JsonConvert.SerializeObject(payload);// Wrap our JSON inside a StringContent which then can be used by the HttpClient classvar httpContent = new StringContent(stringPayload, Encoding.UTF8, "application/json");var httpClient = new HttpClient()    // Do the actual request and await the responsevar httpResponse = await httpClient.PostAsync("http://localhost/api/path", httpContent);// If the response contains content we want to read it!if (httpResponse.Content != null) {    var responseContent = await httpResponse.Content.ReadAsStringAsync();        // From here on you could deserialize the ResponseContent back again to a concrete C# type using Json.Net}

Using the JSON.NET NuGet package and anonymous types, you can simplify what the other posters are suggesting:

// ...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);// ...

You can build your HttpContent using the combination of JObject to avoid and JProperty and then call ToString() on it when building the StringContent:

        /*{          "agent": {                                         "name": "Agent Name",                            "version": 1                                                                    },          "username": "Username",                                             "password": "User Password",          "token": "xxxxxx"        }*/        JObject payLoad = new JObject(            new JProperty("agent",                 new JObject(                    new JProperty("name", "Agent Name"),                    new JProperty("version", 1)                    ),                new JProperty("username", "Username"),                new JProperty("password", "User Password"),                new JProperty("token", "xxxxxx")                    )            );        using (HttpClient client = new HttpClient())        {            var httpContent = new StringContent(payLoad.ToString(), Encoding.UTF8, "application/json");            using (HttpResponseMessage response = await client.PostAsync(requestUri, httpContent))            {                response.EnsureSuccessStatusCode();                string responseBody = await response.Content.ReadAsStringAsync();                return JObject.Parse(responseBody);            }        }