Closes #805 - Unable to signin on self-hosted installations with non-www subdomain

shared/utils/domains.js

@@ -9,6 +9,13 @@ export function stripSubdomain(hostname: string) {
   return parsed.domain;
 }
 
+export function isCustomSubdomain(hostname: string) {
+  const parsed = parseDomain(hostname);
+  if (!parsed) return false;
+  if (!parsed.subdomain || parsed.subdomain === 'www') return false;
+  return true;
+}
+
 export const RESERVED_SUBDOMAINS = [
   'about',
   'account',