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ASP.NET Web API post to an external api

I would like to ask if it is possible for a created ASP.NET Web API (written in C#) to post to an external API?
If it is possible, please share sample code that can post to an url with adding headers and receive a callback from the external API.

A simple way to make HTTP-Request out of a .NET-Application is the System.Net.Http.HttpClient (MSDN). An example usage would look something like this:
// Should be a static readonly field/property, wich is only instanciated once
var client = new HttpClient();
var requestData = new Dictionary<string, string>
{
{ "field1", "Some data of the field" },
{ "field2", "Even more data" }
};
var request = new HttpRequestMessage() {
RequestUri = new Uri("https://domain.top/route"),
Method = HttpMethod.Post,
Content = new FormUrlEncodedContent(requestData)
};
request.Headers // Add or modify headers
var response = await client.SendAsync(request);
// To read the response as string
var responseString = await response.Content.ReadAsStringAsync();
// To read the response as json
var responseJson = await response.Content.ReadAsAsync<ResponseObject>();

Essentially you need use an instance of HttpClient to send an HttpRequestMessage to an endpoint.
Here is an example to post some jsonData to someEndPointUrl:
var client = new HttpClient();
var request = new HttpRequestMessage(HttpMethod.Post, someEndPointUrl);
request.Headers.Accept.Clear();
request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", token);
request.Content = new StringContent(jsonData, Encoding.UTF8, "application/json");
var response = await client.SendAsync(request, CancellationToken.None);
var str = await response.Content.ReadAsStringAsync();
if (response.StatusCode == HttpStatusCode.OK)
{
// handle your response
}
else
{
// or failed response ?
}

How to pass request content with HttpClient GetAsync method in c#

How do I pass request content in the HttpClient.GetAsync method? I need to fetch data depending upon request content.
[HttpGet]
public async Task<HttpResponseMessage> QuickSearch()
{
try
{
using (HttpClient client = new HttpClient())
{
client.DefaultRequestHeaders.Accept.Clear();
HttpResponseMessage response =await client.GetAsync("http://localhost:8080/document/quicksearch");
if (response.IsSuccessStatusCode)
{
Console.Write("Success");
}

If you are using .NET Core, the standard HttpClient can do this out-of-the-box. For example, to send a GET request with a JSON body:
HttpClient client = ...
...
var request = new HttpRequestMessage
{
Method = HttpMethod.Get,
RequestUri = new Uri("some url"),
Content = new StringContent("some json", Encoding.UTF8, ContentType.Json),
};
var response = await client.SendAsync(request).ConfigureAwait(false);
response.EnsureSuccessStatusCode();
var responseBody = await response.Content.ReadAsStringAsync().ConfigureAwait(false);

If you want to send content, then you need to send it as query string (According to your API route)
HttpResponseMessage response =await client.GetAsync("http://localhost:8080/document/quicksearch/paramname=<dynamicName>&paramValue=<dynamicValue>");
And in API check for "paramName" and "paramValue"

this works for me:
using (var httpClient = new HttpClient())
{
var request = new HttpRequestMessage
{
Method = HttpMethod.Get,
RequestUri = new Uri("your url"),
Content = new StringContent("your json", Encoding.UTF8, ContentType.Json),
};
using (var response = await httpClient.SendAsync(request))
{
string apiResponse = await response.Content.ReadAsStringAsync();
}
}
EDITED:
This is minor different then #SonaliJain answer above:
MediaTypeNames.Application.Json instead of ContentType.Json

I'm assuming that your "request content" would be POST data, no?
If you're sending it using the standard form content way of doing it, you would first have to build the content:
var content = new FormUrlEncodedContent(new[]
{
new KeyValuePair<string, string>("username", "theperplexedone"),
new KeyValuePair<string, string>("password", "mypassword123"),
});
And then submit it using PostAsync instead:
var response = await client.PostAsync("http://localhost:8080/document/quicksearch", content);

Hi all thank you for your comments, i got the solution
[HttpGet]
public async Task<HttpResponseMessage> QuickSearch(HttpRequestMessage Query)
{
Debugger.Launch();
try
{
using (HttpClient client = new HttpClient())
{
client.DefaultRequestHeaders.Accept.Clear();
Console.WriteLine(Query);
HttpResponseMessage response = await client.GetAsync("http://localhost:8080/document/quicksearch/"+ Query.RequestUri.Query);
if (response.IsSuccessStatusCode)
{
Console.Write("Success");
}
else
{
Console.Write("Failure");
}
return response;
}
}
catch (Exception e)
{
throw e;
}

Rest POST API working with POSTMAN but not working Xamarin.Forms

Heres the code to my HttpPost request
async void ContinueBtn_Clicked(object sender, EventArgs e)
{
if (!CheckValidation())
{
LoginBLL cust = new LoginBLL();
EncryptPassword encrypt = new EncryptPassword();
cust.name = txtFieldName.Text;
cust.email = txtFieldEmail.Text;
cust.Password = encrypt.HashPassword(txtFieldPass.Text);
cust.profession = txtFieldJob.Text;
cust.company = txtFieldCompany.Text;
cust.subId = 1320;
HttpClient client = new HttpClient();
string url = "https://www.example.com/api/customer/";
var uri = new Uri(url);
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
HttpResponseMessage response;
var json = JsonConvert.SerializeObject(cust);
var content = new StringContent(json, Encoding.UTF8, "application/json");
response = await client.PostAsync(uri, content);
if (response.StatusCode == System.Net.HttpStatusCode.Accepted)
{
validationName.Text = await response.Content.ReadAsStringAsync();
}
else
{
validationName.Text = await response.Content.ReadAsStringAsync();
}
}
And I am getting this error when I am executing the above function
No HTTP resource was found that matches the request URI 'https://www.example.com/api/customer/'.
But it is working fine in Postman with same variables.
I even verified the JSON generated in POSTMAN with the JSON being generated in the Visual Studio it is identical.
I am running this on iphone 8 iOS 12.0

HttpClient sending parameter null

I'm trying to send data to an api with HttpClient but parameter I'm sending keeps received as 0.
What am I doing wrong here? It's my first usage of HttpClient so it's quite possible I mixed things or made some rookie mistake.
Path is correct, I can get results from Postman.
Code I'm using is this;
static async Task GetActivityList()
{
string uri = "/api/ExtraNet/GetActivityList";
HttpClient client = new HttpClient();
int SalesPersonId = 553;
string token = my token value is here;
client.BaseAddress = new Uri("http://localhost:16513/");
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(
new MediaTypeWithQualityHeaderValue("application/json"));
client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);
var postData = "{\"SalesPersonId=\":\""+SalesPersonId+"\"}";
var stringContent = new StringContent( "{\"SalesPersonId=\":\"" + SalesPersonId + "\"}", Encoding.UTF8, "application/json") ;
var content = new StringContent(postData, Encoding.UTF8, "application/json");
var response = await client.PostAsync("http://localhost:16513/api/ExtraNet/GetActivityList", stringContent);
var result = await response.Content.ReadAsStringAsync();
Console.WriteLine(result);
}

I managed to send the parameter this way
string uri = "/api/ExtraNet/GetActivityList";
HttpClient client = new HttpClient();
int SalesPersonId = 553;
string token = "";
client.BaseAddress = new Uri("http://localhost:16513/");
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(
new MediaTypeWithQualityHeaderValue("application/json"));
client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);
var stringContent = new FormUrlEncodedContent(new[] {
new KeyValuePair<string,string>("SalesPersonId","553")
});
var response = await client.PostAsync(uri, stringContent);
var result = await response.Content.ReadAsStringAsync();
Console.WriteLine(result);
Sending the parameters as FormUrlEncodedContent did the trick.

Error on ConfigureAwait(false)

I am trying to retrieve some data from an API, the following is my piece of code that makes the request after authenticating and assigning the completed URL.
public async Task<T> GetAPIData<T>(string url)
{
using (var client = HttpClientSetup())
{
var response = await client.GetAsync(url).ConfigureAwait(false);
var JsonResponse = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
return JsonConvert.DeserializeObject<T>(JsonResponse);
}
}
private HttpClient HttpClientSetup()
{
var client = new HttpClient { BaseAddress = new Uri(apiBaseUrl) };
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
client.DefaultRequestHeaders.Authorization = authenticationHeader;
return client;
}
I am getting an error on the line with ConfigureAwait(false);
as
"HTTPResponseMessage does not contain a definition for ConfigureAwait"
. Could anyone help me as to what might be going wrong?