Has anyone been through the process of creating an OAUTHBEARER token for e-mail to appease the likes of Microsoft and Google?

The Google documentation on doing this via the Cloud Console is rather vague.

I am trying to add the ability to specify a token (or username and token?) to an existing application, not add full OAuth2 support. Doing so requires a token to test with, but so far all attempts have been met with...

 

< 535-5.7.8 Username and Password not accepted. Learn more at
< 535 5.7.8  https://support.google.com/mail/?p=BadCredentials n2-20020a170902d2c200b001715a939ac5sm2638365plc.295 - gsmtp