Office 365 SMTP authentication via XOAUTH2

Question

I'm following this guide https://learn.microsoft.com/en-us/exchange/client-developer/legacy-protocols/how-to-authenticate-an-imap-pop-smtp-application-by-using-oauth and here's all the steps I've taken -

Note: I'm not posting my actual client id's, codes or secrets.

Step 1: Register an Azure app.

Account type: Accounts in this organizational directory only

Redirect URI: http://localhost (Web)

Created a client secret

Added SMTP.Send API permission

Step 2: Request an authorization code

https://login.microsoftonline.com/organizations/oauth2/v2.0/authorize?
client_id=6731de76-14a6-49ae-97bc-6eba6914391e
&response_type=code
&redirect_uri=http://localhost
&response_mode=query
&scope=https://outlook.office.com/SMTP.Send

Step 3: Redeem the authorization code (!!! 793 characters long) for an access token using the client secret

curl -d "client_id=6731de76-14a6-49ae-97bc-6eba6914391e
&scope=https://outlook.office.com/SMTP.Send
&code=OAAABAAAAiL9Kn2Z27UubvWFPbm0gLWQJVzCTE9UkP3pSx1aXxUjq3n8b2JRLk4OxVXr...
&redirect_uri=http://localhost
&grant_type=authorization_code
&client_secret=JqQX2PNo9bpM0uEihUPzyrh" -X POST https://login.microsoftonline.com/organizations/oauth2/v2.0/token

Step 4: Convert the mailbox username and bearer token (!!! 1787 characters long) into a base64 string

echo -n "user=test@contoso.onmicrosoft.com^Aauth=Bearer EwBAAl3BAAUFFpUAo7J3Ve0bjLBWZWCclRC3EoAA^A^A" | base64

The final base64 string is 2464 characters long and obviously WAY too long for SMTP to accept. Where am I going wrong with this?

Answer 1

I found this online that MS has not enabled OAuth for SMTP from the documentation Link

Basic Auth still works for SMTP and will be disabled for IMAP AND POP protocols. Please reply if you have figured out a way to use OAuth for SMTP to send mails.