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Calling an api using httpClient PostAsync - 400 Bad Request

There has been a lot of similar questioning on this one but I could not get any answers working for me..
I am calling another api Post request from my controller..but I get a 400 bad request all the time..
public async Task<JsonResult> TestSCIMPost(AppAuth auth)
{
//Method 3:
HttpClient client = new HttpClient();
var jsonRequest = Newtonsoft.Json.JsonConvert.SerializeObject(auth);
var content = new StringContent(jsonRequest);
content.Headers.Remove("Content-Type");
content.Headers.Add("Content-Type", "application/json");
HttpResponseMessage response = await client.PostAsJsonAsync(
URL, content);
return new JsonResult(response);
}
curl
curl -X POST "https://localhost:5001/api/Employee/api/Employee/TestSCIMPost" -H "accept: /" -H "Content-Type: application/json-patch+json" -d "{"client_id":"xyz","grant_type":"cc","client_secret":"abc","scope":"read"}"
I have tried a couple of other ways that I am listing below..
public async Task<JsonResult> TestSCIMPost(AppAuth auth)
{
/*var response = string.Empty;
var jsonRequest = Newtonsoft.Json.JsonConvert.SerializeObject(auth);
byte[] messageBytes = System.Text.Encoding.UTF8.GetBytes(jsonRequest);
var content = new ByteArrayContent(messageBytes);
//HttpContent c = new StringContent(jsonRequest, Encoding.UTF8, "application/json");
content.Headers.Remove("Content-Type");
content.Headers.Add("Content-Type", "application/json");
//content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
using (var client = new HttpClient())
{
//client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
HttpResponseMessage result = await client.PostAsync(URL, content);
if (result.IsSuccessStatusCode)
{
response = result.StatusCode.ToString();
}
}*/
//Method:2
//HttpClient client = new HttpClient();
//client.BaseAddress = new Uri(URL);
//client.DefaultRequestHeaders.Accept.Clear();
//client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("*/*"));
//var requestMessage = Newtonsoft.Json.JsonConvert.SerializeObject(auth);
//var content = new StringContent(requestMessage, Encoding.UTF8, "application/json");
//content.Headers.Remove("Content-Type");
//content.Headers.Add("Content-Type", "application/json");
//HttpResponseMessage result = await client.PostAsync(URL, content);
return new JsonResult(response);
}
The body is coming from auth (frontend that i am serializing and adding in my request)
What's going wrong here? Is it utf-encoding? how to fix?

One reason this can happen is if you are posting content in the body (as you are doing) where the parser expects to find it in the query.
So if you have something like this:
string url = "https://localhost:5001/api/Employee/TestSCIMPost";
var content = new StringContent("{\"client_id\":\"xyz\",\"grant_type\":\"cc\"}");
HttpResponseMessage response = await client.PostAsync(url, content);
Try changing it to this:
string url = "https://localhost:5001/api/Employee/TestSCIMPost?client_id=xyz&grant_type=cc";
var content = new StringContent("");
HttpResponseMessage response = await client.PostAsync(url, content);

why An error is created when creating the token

public static void CreateToken()
{
HttpClient client = new HttpClient();
client.DefaultRequestHeaders.Add("grant_type", "client_credentials");
var UserPassJson = "{\"username\": \"mucode\",\"password\": \"mypassword\"}";
HttpContent content = new StringContent(UserPassJson, Encoding.UTF8, "application/json");
var response = client.PostAsync(new Uri("https://api.sandbox.paypal.com/v1/oauth2/token"), content).Result;
if (response.IsSuccessStatusCode)
{
var responseContent = response.Content;
string responseString = responseContent.ReadAsStringAsync().Result;
Console.WriteLine(responseString);
}
}
why response.IsSuccessStatusCode Showing status code 401? What causes the malfunction?
What action does cause success?

The documentation specifies that you should pass the username and password using basic authentication and that you should pass a form-encoded body containing grant_type=client_credentials.
At the moment your code adds grant_type as a header, and posts the username and password as a JSON object in the body.
Correcting your code to do it the way the documentation says, we get:
HttpClient client = new HttpClient();
byte[] authBytes = System.Text.Encoding.ASCII.GetBytes("mucode:mypassword");
string base64Auth = Convert.ToBase64String(authBytes);
client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Basic", base64Auth);
HttpContent content = new FormUrlEncodedContent(new[] { new KeyValuePair<string, string>("grant_type", "client_credentials") });
var response = client.PostAsync(new Uri("https://api.sandbox.paypal.com/v1/oauth2/token"), content).Result;
if (response.IsSuccessStatusCode)
{
var responseContent = response.Content;
string responseString = responseContent.ReadAsStringAsync().Result;
Console.WriteLine(responseString);
}
P.S. I recommend reading You're using HttpClient wrong and it is destabilizing your software and the follow-up You're (probably still) using HttpClient wrong and it is destabilizing your software. I also recommend making this method async and making the chain all the way up async too.

How to read/output response from the HTTP request

I send HTTP request to a webpage to insert or retrieve data.
This is my code:
string json = JsonConvert.SerializeObject(user);
using (var client = new HttpClient())
{
var response = client.PostAsync(
"url",
new StringContent(json, Encoding.UTF8, "application/json"));
}
DisplayAlert("Alert", json, "OK");
DisplayAlert("test", response, "test");
For this particular example; the website should return true or false.
But I want to read the response variable.
The DisplayAlert("test", response, "test"); show error. And this is because I am trying to read response outside of scope.
My question is how to read the response variable or output response variable on the page?
Edit
{
LoginModel user = new LoginModel();
{
user.email = email.Text;
user.password = password.Text;
};
string json = JsonConvert.SerializeObject(user);
using (var client = new HttpClient())
{
}
var response = client.PostAsync(
"https://scs.agsigns.co.uk/tasks/photoapi/login-photoapi/login-check.php",
new StringContent(json, Encoding.UTF8, "application/json"));
DisplayAlert("Alert", json, "OK");
DisplayAlert("test", response, "test");
}

This gives you an error because you try to access a variable which is declared inside of a different scope. If you move the variable response inside of the "method scope" the error will disappear:
string json = JsonConvert.SerializeObject(user);
HttpResponseMessage response;
using (var client = new HttpClient())
{
response = await client.PostAsync(
"url",
new StringContent(json, Encoding.UTF8, "application/json"));
}
DisplayAlert("Alert", json, "OK");
DisplayAlert("test", await response.Content.ReadAsStringAsync(), "test");
Note the await which I added just before client.PostAsync() (You will find more infos about async/await in the docs).
To get the string representation of the response content you can use following method:
await response.Content.ReadAsStringAsync();
This will read the response content as string.

string json = JsonConvert.SerializeObject(user);
HttpResponseMessage response;
using (var client = new HttpClient())
{
response = client.PostAsync(
"url",
new StringContent(json, Encoding.UTF8, "application/json").Result);
}
var body = response.Content.ReadAsStringAsync().Result;
DisplayAlert("Alert", json, "OK");
DisplayAlert("test", body, "test");
should work, by moving the declaration of the variable outside the scope, and updating the value inside the call.

Strange behavior in HttpRequestMessage's Content-Type header

I tried to make HTTP POST request with application/json in body to an external web-service from C# (.NET Core 2.2.104).
I've already read all similar questions in SO and wrote this code:
SignXmlRequestDto requestBody = new SignXmlRequestDto(p12, model.SignCertPin, model.Data);
string json = JsonConvert.SerializeObject(requestBody);
var httpRequestMessage = new HttpRequestMessage
{
Method = HttpMethod.Post,
RequestUri = ncanNodeUrl,
Headers =
{
{ HttpRequestHeader.ContentType.ToString(), "application/json" }
},
Content = new StringContent(JsonConvert.SerializeObject(json))
};
var response = await httpClient.SendAsync(httpRequestMessage);
string responseString = await response.Content.ReadAsStringAsync();
I am getting an error from service, it says: "Invalid header Content-Type. Please set Content-Type to application/json". What is interesting here, if I simulate this request from Postman, then everything work well and I get successful response.
Updated: as #Kristóf Tóth suggested, I modified my code to:
var httpRequestMessage = new HttpRequestMessage
{
Method = HttpMethod.Post,
RequestUri = ncanNodeUrl,
Content = new StringContent(json, Encoding.UTF8, "application/json")
};
var response = await httpClient.SendAsync(httpRequestMessage);
string responseString = await response.Content.ReadAsStringAsync();
but it still gives me the same error message.

Content-Type is a content header. It should be set on the content, not the request itself. This can be done either using the StringContent(string,Encoding,string) constructor :
Content = new StringContent(JsonConvert.SerializeObject(json),Encoding.UTF8, "application/json")
or by setting the StringContent's Headers.ContentType property :
var content=new StringContent(JsonConvert.SerializeObject(json));
content.Headers.ContentType = new MediaTypeHeaderValue("application/json");

This might be an encoding issue. You should use JsonContent not StringContent OR you can do something similar:
// Serialize into JSON String
var stringPayload = JsonConvert.SerializeObject(payload);
// Wrap JSON StringContent which then can be used by the HttpClient class
var httpContent = new StringContent(stringPayload, Encoding.UTF8, "application/json");

C# HttpClient POST request pass already encoded data

I have already encoded data that wants to pass as is the String to HttpClient PostRequest
but FormUrlEncodedContent only accepts a dictonary as parameter
I want something like client.PostAsync(url, plain_string_content)
var content = new FormUrlEncodedContent(values);
using (var client = new HttpClient())
{
try
{
var response = client.PostAsync(url, content).GetAwaiter().GetResult();
string resp=response.Content.ReadAsStringAsync().GetAwaiter().GetResult();
return resp;
}

You may use HttpClient.SendAsync:
HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post);
request.Content = new StringContent(plain_string_content);
request.Content.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded");
await client.SendAsync(request);
Note that, after all, PostAsync and other HttpClient's methods are shortcuts of SendAsync.