fix(plugin): preserve default headers (fixes #323)

Author: pooya parsa

Diff for: lib/plugin.js

@@ -197,9 +197,14 @@ export default (ctx, inject) => {
 
   <% if (options.proxyHeaders) { %>
   // Proxy SSR request headers headers
-  axiosOptions.headers.common = (ctx.req && ctx.req.headers) ? Object.assign({}, ctx.req.headers) : {}
-  <% for (let h of options.proxyHeadersIgnore) { %>delete axiosOptions.headers.common['<%= h %>']
-  <% } %><% } %>
+  if (process.server && ctx.req && ctx.req.headers) {
+    const reqHeaders = { ...ctx.req.headers }
+    for (let h of <%= serialize(options.proxyHeadersIgnore) %>) {
+      delete reqHeaders[h]
+    }
+    axiosOptions.headers.common = { ...reqHeaders, ...axiosOptions.headers.common }
+  }
+  <% } %>
 
   if (process.server) {
     // Don't accept brotli encoding because Node can't parse it