GraphAuthService.cs

using System;
using Microsoft.Extensions.Configuration;
using Microsoft.Graph;
using Microsoft.Graph.Auth;
using Microsoft.Identity.Client;

namespace < YOURNAMESPACE > {
	public interface IGraphAuthService {
		GraphServiceClient GetGraphServiceClient(Guid tenantId);
	}
	public class GraphAuthService: IGraphAuthService {
		private readonly IConfiguration _configuration;

		public GraphAuthService(IConfiguration configuration) {
			_configuration = configuration;
		}

		private ClientCredentialProvider GetGraphAuthProvider(Guid tenantId) {
			IConfidentialClientApplication confidentialClientApplication = ConfidentialClientApplicationBuilder
				.Create(_configuration["AzureAd:ClientId"])
				.WithTenantId(Convert.ToString(tenantId))
				.WithClientSecret(_configuration["GraphClientSecret"])
				.Build();
			return new ClientCredentialProvider(confidentialClientApplication);
		}

		public GraphServiceClient GetGraphServiceClient(Guid tenantId) = >new GraphServiceClient(GetGraphAuthProvider(tenantId));
	}
}