[PR] fix(providers/smtp): fix OAuth2 XOAUTH2 auth and EHLO after STARTTLS in SmtpHook [airflow]

["YoannAbriel (via GitHub)" <gi...@apache.org>]

YoannAbriel opened a new pull request, #62879:
URL: https://github.com/apache/airflow/pull/62879

   ## Problem
   
   When using `SmtpHook` with `auth_type="oauth2"` against a server that requires STARTTLS (e.g., Microsoft 365 / smtp.office365.com:587), sending an email fails with `530 5.7.57 Client not authenticated to send mail`. The XOAUTH2 AUTH command succeeds, but the subsequent MAIL FROM is rejected because the SMTP session state was reset by STARTTLS without a follow-up EHLO.
   
   ## Root Cause
   
   Three separate bugs in `SmtpHook`:
   
   1. **`get_conn()` uses `self._auth_type` instead of `self.auth_type` property.** The `auth_type` property reads from connection extras and falls back to the constructor argument. Using the raw `_auth_type` attribute means setting `auth_type` in the connection extras JSON has no effect — the constructor default `"basic"` always wins.
   
   2. **Missing `ehlo()` after `starttls()`.** Per RFC 3207, after STARTTLS completes, the client must re-issue EHLO to re-establish the session. Without it, the server considers the session unauthenticated after AUTH succeeds, causing MAIL FROM to be rejected.
   
   3. **Async path (`aget_conn`) has no OAuth2 support.** It only handles basic auth via `auth_login`, silently ignoring `auth_type="oauth2"`.
   
   ## Fix
   
   - Changed `self._auth_type` to `self.auth_type` in `get_conn()` so connection extras are respected.
   - Added `self._smtp_client.ehlo()` after `starttls()` in both sync and async paths.
   - Added OAuth2/XOAUTH2 authentication support to `aget_conn()`, mirroring the sync implementation.
   - Added tests for all three fixes: auth_type property usage, ehlo-after-starttls ordering, and async OAuth2 auth.
   
   Closes: #62775
   
   <!-- SPDX-License-Identifier: Apache-2.0
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Re: [PR] fix(providers/smtp): fix OAuth2 XOAUTH2 auth and EHLO after STARTTLS in SmtpHook [airflow]

["dabla (via GitHub)" <gi...@apache.org>]

dabla merged PR #62879:
URL: https://github.com/apache/airflow/pull/62879


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