Email sending service (non user inactive) - OAuth2 microsoft c# send mailkit

Question

I am trying to replace a windows service which sends emails for users via smtp with Microsoft accounts (within the business)

Microsoft are turning off the old auth method at the end of the month

I am using c# and mail kit and can get a token, however I can not currently send emails without user interaction to 'sign in via a webpage' each time to grant permission

Ofcourse a windows service on another box can not interact with the users

I have registered my app via azure, that part seems done

I have searched the web and find a lot of mixed results

Is anyone aware, Is it currently possible to have a windows service (without user interaction) send emails on a users behalf (I have their user/pass etc) but can not see a clear way to do this using mailkit

Thank You

Answer 1

it appears that user:sendmail has application permission. https://learn.microsoft.com/en-us/graph/api/user-sendmail?view=graph-rest-1.0&tabs=http

meaning you can register your application with a client secret and then use the client secret to make calls to graph without the need for user interaction.

you can most of this from the graph quick start https://developer.microsoft.com/en-us/graph/quick-start

I am working on something similar where I am making graph calls through a c# api but probably similiar.

I have my registration info in appsettings.

 "Settings": {
    "clientId": "7d202de8-ccd8-xxxxxxxx-a5e4-101df736dd6a",
    "clientSecret": "ctV8Q~U3qYHpd_xxxxxxOeHB08TXxxxxxxxxU_.ag9",
    "tenantId": "44fxxxxxx5-327a-4d5a-86d5-cxxxxxxxxx97d7e4"
  },

I have a helper class that makes the api calls (this one is getting some users)

namespace Application
{
    using Azure.Identity;
    using Microsoft.Graph;
    public class GraphHelper
    {
        private static Settings _settings;

        public static void InitializeGraph(Settings settings,
    Func<DeviceCodeInfo, CancellationToken, Task> deviceCodePrompt)
        {
            _settings = settings;
        }

        private static ClientSecretCredential _clientSecretCredential;
        private static GraphServiceClient _appClient;

        private static void EnsureGraphForAppOnlyAuth()
        {
            _ = _settings ??
                throw new System.NullReferenceException("Settings cannot be null");

            if (_clientSecretCredential == null)
            {
                _clientSecretCredential = new ClientSecretCredential(
                    _settings.TenantId, _settings.ClientId, _settings.ClientSecret);
            }

            if (_appClient == null)
            {
                _appClient = new GraphServiceClient(_clientSecretCredential,
                    new[] { "https://graph.microsoft.com/.default" });
            }
        }

        public static Task<IGraphServiceUsersCollectionPage> GetUsersAsync()
        {
            EnsureGraphForAppOnlyAuth();
            _ = _appClient ??
                throw new System.NullReferenceException("Graph has not been initialized for app-only auth");

            return _appClient.Users
                .Request()
                .Select(u => new
                {
                    // Only request specific properties
                    u.DisplayName,
                    u.Id,
                    u.Mail
                })
                // Get at most 25 results
                .Top(25)
                // Sort by display name
                .OrderBy("DisplayName")
                .GetAsync();
        }
}
}
 

then I can make calls to it like this

public async Task<IGraphServiceUsersCollectionPage> Handle(Query request, CancellationToken cancellationToken)
            {
                Settings s = new Settings();
                var settings = s.LoadSettings(_config);
                GraphHelper.InitializeGraph(settings, (info, cancel) => Task.FromResult(0));
                var result = await GraphHelper.GetUsersAsync();
                return result;
            }