I have a web application that sends e-mails to users via Exchange Online (Office365) using MailKit and Basic Authentication. Our company is MS partner and therefor is obligated to turn off Basic Authentication for our services by the end of february 2020.
So, I want to use OAuth 2.0 to connect to Exchange Online, similar to this example. In fact, there might be a solution available according to this answer but I'm unable to find anything about it.
Right now I'm playing around with MS Identity Platform v2.0 but I'm unable to figure out how to do it.
Any help would be appriciated.
UPDATE 1
I do not want to send mails on behalf of signed-in users but instead there is a single Office365 user account that shall be used to send mails (notifications and so on) to others.
UPDATE 2
I managed to get a little closer to what I want to do using Microsoft Graph SDK and the Username/Password Provider.
Our user account requires multifactor-authentication and therefor I get an error when using the user's password since I cannot satisfy the second factor. When I'm using an app-password authentication fails because of incorrect password.
UPDATE 3
I switched to mail relaying for now. But I will update this question if I'll ever find an answer to it.
Using the Microsoft.Identity.Client you can generate a token and pass though then authentication using that.
I spotted the below for IMAP, POP3 and SMTP so adapted for my project to get a working solution. Although the example show the interactive method, where as I am was trying to use the the client credentials flow with an app secret.
MailKit - Using OAuth2 With Exchange (IMAP, POP3 or SMTP)
Microsoft - Authenticate an IMAP, POP or SMTP connection using OAuth
From @hB0 comment
Setting up Service Principles via client credentials grant flow (non-interactive)