C# Post Variables can't be read on Website - HttpClient PostAsync()

Question

I have a web server on which I'm hosting my own api for one of my projects. This is the php-code of the api-website:

$user = $_POST['username'];
$password = $_POST['password'];
if(strcmp($user, "username") == 0 && strcmp($password, "password") == 0) {
    ...
} else {
    die("No Permissions");
}

I want to send the two variables username and password with a HttpClient and the postAsync-method to this website and if the right log in data is detected, it returns the data I want. For this I have the following code in C#:

Task<HttpResponseMessage> response;
var url = "www.url.de"; //not the url I'm actually calling!
var vars = "[{\"username\":\"username\", \"password\":\"password\"}]";
using (var client = new HttpClient())
{
   client.BaseAddress = new Uri(url);
   client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
   response = client.PostAsync(url, new StringContent(vars, Encoding.UTF8));
   Console.WriteLine(response.Result.Content.ReadAsStringAsync().Result);
   if (response.IsCompleted)
   {
      Console.WriteLine(response.Result.Content.ReadAsStringAsync().Result);
   }
}

But the problem is that no matter what I have tried the output from this code is, that i have no permissions. And I have changed the php-code, so that I can see which data is stored in $username and $password, but they are empty and I don't know why. I hope somebody can help me with this.

Answer 1

Your PHP code is expecting the data sent as application/x-www-form-urlencoded, but your C# code is sending it as JSON.

As mentioned in the comment by M. Eriksson, you either need to change your PHP to accept JSON, or change your C# to send as form data.

This answer shows how to use HTTPClient to send data like that.

Here's my modification of your code based on the above code (I did test it):

public static async Task DoSomething()
{
    string url = "http://httpbin.org/post"; //not the url I'm actually calling!
    Dictionary<string, string> postData = new();
    postData["username"] = "username";
    postData["password"] = "password";

    using HttpClient client = new();
    
    client.DefaultRequestHeaders.Accept.Add(new("application/json"));

    HttpRequestMessage request = new(HttpMethod.Post, url);
    request.Content = new FormUrlEncodedContent(postData);

    HttpResponseMessage response = await client.SendAsync(request);
    
    Console.WriteLine(response.Content.ReadAsStringAsync().Result);
}