consider some config keys under 'objectstore_multibucket' as sensitive

Signed-off-by: Julien Veyssier <eneiluj@posteo.net>

lib/private/SystemConfig.php

@@ -84,6 +84,27 @@ class SystemConfig {
 				],
 			],
 		],
+		'objectstore_multibucket' => [
+			'arguments' => [
+				'options' => [
+					'credentials' => [
+						'key' => true,
+						'secret' => true,
+					]
+				],
+				// S3
+				'key' => true,
+				'secret' => true,
+				// Swift v2
+				'username' => true,
+				'password' => true,
+				// Swift v3
+				'user' => [
+					'name' => true,
+					'password' => true,
+				],
+			],
+		],
 	];
 
 	/** @var Config */