This is a minor feature release.
> Prior to this version, any OAuth provider needed to extend the provided `OAuth` base class, and this made it difficult to use with libraries other than ones based on the default [https://github.com/thephpleague/oauth2-client league] client packages. The OAuth property now accepts anything that implements the `OAuthProviderInterface`, making it much easier to use things like [https://github.com/googleapis/google-api-php-client Google's own OAuth classes]. Existing implementations that extend the provided `OAuth` base class will still work, as that base class now implements this interface too.
>
> When TLS errors occurred in PHPMailer, the error messages were often missing important info that might help diagnose/solve the problem. These error messages should now be more informative. A minor change is that a TLS error on SMTP connect will now throw an exception if exceptions are enabled.
Release notes:
https://github.com/PHPMailer/PHPMailer/releases/tag/v6.6.0
For a full list of changes in this update, see the PHPMailer GitHub:
https://github.com/PHPMailer/PHPMailer/compare/v6.5.4...v6.6.0
Follow-up to [50628], [50799], [51169], [51634], [51635], [52252], [52749].
Props jrf, Synchro, miken32.
Fixes#55277.
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