Add getBackupCredentials to backups API

src/backups.js

@@ -10,7 +10,9 @@ exports = module.exports = {
     getAppBackupUrl: getAppBackupUrl,
     getRestoreUrl: getRestoreUrl,
 
-    copyLastBackup: copyLastBackup
+    copyLastBackup: copyLastBackup,
+
+    getBackupCredentials: getBackupCredentials
 };
 
 var assert = require('assert'),
@@ -79,6 +81,20 @@ function getByAppIdPaged(page, perPage, appId, callback) {
     });
 }
 
+function getBackupCredentials(callback) {
+    assert.strictEqual(typeof callback, 'function');
+
+    settings.getBackupConfig(function (error, backupConfig) {
+        if (error) return callback(new BackupsError(BackupsError.INTERNAL_ERROR, error));
+
+        api(backupConfig.provider).getBackupCredentials(backupConfig, function (error, credentials) {
+            if (error) return callback(error);
+
+            return callback(null, credentials);
+        });
+    });
+}
+
 function getBackupUrl(appBackupIds, callback) {
     assert(util.isArray(appBackupIds));
     assert.strictEqual(typeof callback, 'function');