RequestUpload.cs

	// files: suppose we have a list of file paths
	// subDirectory: the sub-directory structure under root for storing
	public async Task<HttpResponseMessage> UploadFilesAsync(List<string> files, string subDirectory)
	{
		string boundary = $"--{DateTime.Now.Ticks:x}";
                using var content = new MultipartFormDataContent(boundary);
            	content.Headers.Add("ContentType", $"multipart/form-data, boundary={boundary}");
		foreach (var filePath in files)
		{
			content.Add(new StringContent(subDirectory, Encoding.UTF8), "subDirectory");

			using var stream = new FileStream(filePath, FileMode.Open, FileAccess.Read);
			var fileNameHash = Path.GetFileNameWithoutExtension(filePath) + "_" + Guid.NewGuid().ToString("N") + Path.GetExtension(filePath);
			content.Add(new StreamContent(stream), "files", fileNameHash);
		
		}
		
		// IHttpClientFactory, consider using factory would be more effeicecy 
		var httpClient = new HttpClient();
		using HttpRequestMessage request = new(HttpMethod.Post, new Uri("{your file API uri}")) { Content = content };
		// fire the post with the MultipartFormDataContent to File API
		var result = await httpClient.SendAsync(request);
		
		return result;
		
	}