Allow "use_authorization_to_get_token" to be configured to false for …

…generic OAuth2

Backport of the fix #1879  for branch 2.0

src/DependencyInjection/Configuration.php

@@ -227,7 +227,12 @@ private function addResourceOwnersConfiguration(ArrayNodeDefinition $node): void
                             ->end()
                             ->scalarNode('use_authorization_to_get_token')
                                 ->validate()
-                                    ->ifEmpty()
+                                    ->ifTrue(function ($v) {
+                                        if (false === $v) {
+                                            return false;
+                                        }
+                                        return empty($v);
+                                    })
                                     ->thenUnset()
                                 ->end()
                             ->end()