url: keep auth in url.resolve() if host matches

Fixes: nodejs#8165

PR-URL: nodejs#8215
Reviewed-By: James M Snell <[email protected]>

Author: imyller

lib/url.js

@@ -775,13 +775,13 @@ Url.prototype.resolveObject = function(relative) {
   if (isRelAbs) {
     // it's absolute.
     if (relative.host || relative.host === '') {
+      if (result.host !== relative.host) result.auth = null;
       result.host = relative.host;
       result.port = relative.port;
-      result.auth = null;
     }
     if (relative.hostname || relative.hostname === '') {
+      if (result.hostname !== relative.hostname) result.auth = null;
       result.hostname = relative.hostname;
-      result.auth = null;
     }
     result.search = relative.search;
     result.query = relative.query;

test/parallel/test-url.js

@@ -1571,6 +1571,9 @@ var relativeTests2 = [
   ['mailto:another.host.com',
    'mailto:[email protected]',
    'mailto:another.host.com'],
+  ['https://example.com/foo',
+   'https://user:[email protected]',
+   'https://user:[email protected]/foo'],
 ];
 relativeTests2.forEach(function(relativeTest) {
   const a = url.resolve(relativeTest[1], relativeTest[0]);