Add dns interface api to inject hidden files for verification

src/dns/interface.js

@@ -8,6 +8,7 @@
 
 exports = module.exports = {
     removePrivateFields: removePrivateFields,
+    injectPrivateFields: injectPrivateFields,
     upsert: upsert,
     get: get,
     del: del,
@@ -23,6 +24,10 @@ function removePrivateFields(domainObject) {
     return domainObject;
 }
 
+function injectPrivateFields(newConfig, currentConfig) {
+    // in-place injection of tokens and api keys which came in with domains.SECRET_PLACEHOLDER
+}
+
 function upsert(domainObject, location, type, values, callback) {
     assert.strictEqual(typeof domainObject, 'object');
     assert.strictEqual(typeof location, 'string');