Allow for settings-based overrides

Just in case someone finds this useful. I put the client id and secret into config (since that's easy to override by environment) and used the following hook:

/**
 * Implements hook_ENTITY_TYPE_load().
 */
function mymodule_consumer_load($entities): void {
  /** @var \Drupal\consumers\Entity\ConsumerInterface $consumer */
  foreach ($entities as $consumer) {
    if ($consumer->uuid() !== SomeClass::UUID_CONSTANT) {
      continue;
    }
    
    $config = \Drupal::config('mymodule.settings');
    if ($config->get('oauth_client_id')) {
      $consumer->set('client_id', $config->get('oauth_client_id'));
    }
    if ($config->get('oauth_client_secret')) {
      $hash = \Drupal::service('password')->hash(trim($config->get('oauth_client_secret')));
      $consumer->set('secret', $hash);
    }
  }
}

Unfortunately, I wasn't able to get the overriding of the consumer settings working from comment #8 for 2 reasons.

Firstly when updating the 'secret', the BaseFieldDefinition provided by the simple_oauth is a password field type. Therefore the password hashing is handled on saving the consumer (ie by using $consumer->set('secret', 'plain_text_secret');).

Secondly, the secret was updated on each entity load, meaning a new hash was generated... which caused my client_credentials authentication to fail.

However, it steered me in the right direction. I created a drush command to implement the above, which I run whenever I copy 'Live' back to a 'Pre-production' site.