Revision on Yii

In the web service on Yii, a mailing list was created via the SMTP protocol - the services sent an email notification to the Google Mail account, which forwarded this letter to the desired address
- Google has banned mailing through login and password, you need to switch to OAuth 2 authorization protocol.
Have to:
- Switch to the new protocol, mail notifications from Yii service should be sent correctly
- Do it at a reasonable time
What there is:
- There is a web service on Yii with all the accesses and repository (including the test version)
- There is a gmail account through which the forwarding of messages via SMTP is implemented
- Description of the problem, understanding of how to solve it
- Money, payment by card