how to request the Azure token using IdentityClient

TokenProvider.cs

using IdentityModel.Client;
using Microsoft.Extensions.Options;
using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;

namespace Transport
{
        // from the IdentityServer4.Samples\Quickstarts\1_ClientCredentials\src\Client\
	public class TokenProvider
	{
		static readonly ILog Log = LogProvider.GetCurrentClassLogger();

		private readonly IOptions<OAuthConfig> config;

		public TokenProvider(IOptions<OAuthConfig> config)
		{
			this.config = config;
		}

		public async Task<string> GetAsync()
		{
			//https://github.com/AzureAD/microsoft-authentication-library-for-js/issues/560
			
			var config = this.config.Value;
			Log.TraceFormat("loading token from {0} for {1}", config.GetAuthority(), config.Resource);

			using (var client = new HttpClient())
			{
				// discover endpoints from metadata
				var ddr = new DiscoveryDocumentRequest
				{
					Address = config.GetAuthority(),
					Policy = new DiscoveryPolicy { ValidateEndpoints = false } // login.microsoftonline.com provides invalid oauth2 endpoint 
				};
				var disco = await client.GetDiscoveryDocumentAsync(ddr);
				if (disco.IsError)
					throw new ApplicationException($"disco error:{disco.Error}, code:{disco.ErrorType}");

				var tr = await GetAsync(disco.TokenEndpoint, config.ClientId, config.Secret, config.GetScope());
				return tr.AccessToken;
			}
		}

		public async Task<TokenResponse> GetAsync (string tokenEndpoint, string client, string secret, string scope)
		{
			using (var http = new HttpClient())
			{           
				//request token
				var tokenResponse = await http.RequestClientCredentialsTokenAsync(new ClientCredentialsTokenRequest
				{
					Address = tokenEndpoint,
					ClientId = client,
					ClientSecret = secret,
					GrantType = "client_credentials",

					Scope = scope,
				});

				if (tokenResponse.IsError)
					throw new ApplicationException($"token eror:{tokenResponse.Error}, descr:{tokenResponse.ErrorDescription}");

				return tokenResponse;
			}
		}
	}
}