Implement field constraint to restrict request status transitions
>>> [!note] Migrated issue
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<!-- Migrated from issue #3555196. -->
Reported by: [herved](https://www.drupal.org/user/2197136)
Related to !22
>>>
<h3 id="summary-problem-motivation">Problem/Motivation</h3>
<p>There is currently nothing that prevents invalid status transitions of client requests on entity save.</p>
<h3 id="summary-proposed-resolution">Proposed resolution</h3>
<p>- Implement entity constraint to restrict request status transitions.<br>
- Allowed transitions:<br>
-- pending > active<br>
-- pending > rejected<br>
-- rejected > active<br>
- Update/remove <code>OauthClientRequestForm::validateStatusTransition</code><br>
- Update tests - see \Drupal\Tests\oauth_client\Functional\OauthClientTest::testUserJourney</p>
issue