HttpClientExtensions.cs

using System.Collections.Generic;
using Newtonsoft.Json;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using Newtonsoft.Json.Converters;

namespace ArchDev
{
	public static class HttpClientExtensions
	{
		private static JsonSerializerSettings JsonSerializerSettings()
		{
			return new JsonSerializerSettings
			{
				Converters = new List<JsonConverter> { new StringEnumConverter() }
			};
		}

		public static async Task<T> GetAsync<T>(this HttpClient httpClient, string url)
		{
			var response = await httpClient.GetAsync(url);
			if (response.IsSuccessStatusCode)
			{
				var result = await response.Content.ReadAsStringAsync();
				var data = JsonConvert.DeserializeObject<T>(result, JsonSerializerSettings());
				return data;
			}
			return default;
		}

		public static async Task<T> PostAsync<T>(this HttpClient httpClient, string url, object request)
		{
			var serialised = JsonConvert.SerializeObject(request, JsonSerializerSettings());
			var content = new StringContent(serialised, Encoding.UTF8, "application/json");

			var response = await httpClient.PostAsync(url,content);
			if (response.IsSuccessStatusCode)
			{
				var result = await response.Content.ReadAsStringAsync();
				var data = JsonConvert.DeserializeObject<T>(result, JsonSerializerSettings());
				return data;
			}
			return default;
		}

		public static async Task<T> PostFormAsync<T>(this HttpClient httpClient, string url, MultipartFormRequest request)
		{
			var multipartFormDataContent = new MultipartFormDataContent();

			if (request.File != null)
			{
				var streamContent = new StreamContent(request.File.OpenReadStream());
				var fileContent = new ByteArrayContent(await streamContent.ReadAsByteArrayAsync());
				multipartFormDataContent.Add(fileContent, "\"file\"", request.File.FileName);
			}

			var serialised = JsonConvert.SerializeObject(request.Body, JsonSerializerSettings());
			var stringContent = new StringContent(serialised,Encoding.UTF8, "application/json");
			
			multipartFormDataContent.Add(stringContent, "\"body\"");

			var response = await httpClient.PostAsync(url, multipartFormDataContent);
			if (response.IsSuccessStatusCode)
			{
				var result = await response.Content.ReadAsStringAsync();
				var data = JsonConvert.DeserializeObject<T>(result, JsonSerializerSettings());
				return data;
			}
			return default;
		}

		public static async Task<bool> PatchAsync(this HttpClient httpClient, string url, object request)
		{
			var serialised = JsonConvert.SerializeObject(request, JsonSerializerSettings());
			var content = new StringContent(serialised, Encoding.UTF8, "application/json");

			var response = await httpClient.PatchAsync(url, content);
			return response.IsSuccessStatusCode;
		}

		public static async Task<T> PutAsync<T>(this HttpClient httpClient, string url, object request)
		{
			var serialised = JsonConvert.SerializeObject(request, JsonSerializerSettings());
			var content = new StringContent(serialised, Encoding.UTF8, "application/json");

			var response = await httpClient.PutAsync(url, content);
			if (response.IsSuccessStatusCode)
			{
				var result = await response.Content.ReadAsStringAsync();
				var data = JsonConvert.DeserializeObject<T>(result, JsonSerializerSettings());
				return data;
			}
			return default;
		}
	}
}

MultipartFormRequest.cs

using Microsoft.AspNetCore.Http;

namespace ArchDev
{
	public class MultipartFormRequest
	{
		public IFormFile File { get; set; }

		public object Body { get; set; }
	}
}