Redirects in maintenace mode cause fatal errors

[Ambient-Impact]

This is unlikely to be due to moving the DigitalOcean site from preview.omnipedia.app to omnipedia.app because I can replicate this locally on my dev copy of the site.

There seem to be a number of Drupal core issues kind of related but not exactly matching our problem:

• https://www.drupal.org/project/drupal/issues/2934045
• https://www.drupal.org/project/drupal/issues/3275491
• Core search for maintenance redirect bugs
• Google search

Stack trace:

User error: Redirects to external URLs are not allowed by default, use \Drupal\Core\Routing\TrustedRedirectResponse for it. in Drupal\Core\EventSubscriber\RedirectResponseSubscriber->checkRedirectUrl() (line 89 of /var/www/html/web/core/lib/Drupal/Core/EventSubscriber/RedirectResponseSubscriber.php)

#0 /var/www/html/web/core/includes/bootstrap.inc(164): _drupal_error_handler_real(256, 'Redirects to ex...', '/var/www/html/w...', 89)

#1 [internal function]: _drupal_error_handler(256, 'Redirects to ex...', '/var/www/html/w...', 89)

#2 /var/www/html/web/core/lib/Drupal/Core/EventSubscriber/RedirectResponseSubscriber.php(89): trigger_error('Redirects to ex...', 256)

#3 [internal function]: Drupal\Core\EventSubscriber\RedirectResponseSubscriber->checkRedirectUrl(Object(Symfony\Component\HttpKernel\Event\ResponseEvent), 'kernel.response', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher))

#4 /var/www/html/web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php(111): call_user_func(Array, Object(Symfony\Component\HttpKernel\Event\ResponseEvent), 'kernel.response', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher))

#5 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(199): Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object(Symfony\Component\HttpKernel\Event\ResponseEvent), 'kernel.response')

#6 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(250): Symfony\Component\HttpKernel\HttpKernel->filterResponse(Object(Symfony\Component\HttpFoundation\RedirectResponse), Object(Symfony\Component\HttpFoundation\Request), 1)

#7 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(89): Symfony\Component\HttpKernel\HttpKernel->handleThrowable(Object(Drupal\Core\Http\Exception\CacheableAccessDeniedHttpException), Object(Symfony\Component\HttpFoundation\Request), 1)

#8 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/Session.php(58): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)

#9 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(48): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)

#10 /var/www/html/web/core/modules/ban/src/BanMiddleware.php(50): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)

#11 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(48): Drupal\ban\BanMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)

#12 /var/www/html/web/modules/contrib/trusted_reverse_proxy/src/StackMiddleware/TrustedReverseProxyMiddleware.php(64): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)

#13 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(51): Drupal\trusted_reverse_proxy\StackMiddleware\TrustedReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)

#14 /var/www/html/web/modules/contrib/remove_http_headers/src/StackMiddleware/RemoveHttpHeadersMiddleware.php(49): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)

#15 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/StackedHttpKernel.php(51): Drupal\remove_http_headers\StackMiddleware\RemoveHttpHeadersMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)

#16 /var/www/html/web/core/lib/Drupal/Core/DrupalKernel.php(704): Drupal\Core\StackMiddleware\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)

#17 /var/www/html/web/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request))

#18 @main.