refactor: packagist auth (#3809)

lib/datasource/packagist/index.js

@@ -13,14 +13,11 @@ module.exports = {
 
 function getHostOpts(url) {
   const opts = {
-    ...hostRules.find({ hostType: 'packagist', url }),
     json: true,
   };
-  if (opts && opts.username && opts.password) {
-    const auth = Buffer.from(`${opts.username}:${opts.password}`).toString(
-      'base64'
-    );
-    opts.headers = { Authorization: `Basic ${auth}` };
+  const { username, password } = hostRules.find({ hostType: 'packagist', url });
+  if (username && password) {
+    opts.auth = `${opts.username}:${opts.password}`;
   }
   return opts;
 }