Add dns interface api to inject hidden files for verification

src/dns/namecom.js

@@ -2,6 +2,7 @@
 
 exports = module.exports = {
     removePrivateFields: removePrivateFields,
+    injectPrivateFields: injectPrivateFields,
     upsert: upsert,
     get: get,
     del: del,
@@ -30,6 +31,10 @@ function removePrivateFields(domainObject) {
     return domainObject;
 }
 
+function injectPrivateFields(newConfig, currentConfig) {
+    if (newConfig.token === domains.SECRET_PLACEHOLDER) newConfig.token = currentConfig.token;
+}
+
 function addRecord(dnsConfig, zoneName, name, type, values, callback) {
     assert.strictEqual(typeof dnsConfig, 'object');
     assert.strictEqual(typeof zoneName, 'string');