Finish preliminary loop on SSH certificates

backend/src/ee/services/ssh-certificate-template/ssh-certificate-template-validators.ts

@@ -0,0 +1,14 @@
+// Validates usernames or wildcard (*)
+export const isValidUserPattern = (value: string): boolean => {
+  // Matches valid Linux usernames or a wildcard (*)
+  const userRegex = /^(?:\*|[a-z_][a-z0-9_-]{0,31})$/;
+  return userRegex.test(value);
+};
+
+// Validates hostnames, wildcard domains, or IP addresses
+export const isValidHostPattern = (value: string): boolean => {
+  // Matches FQDNs, wildcard domains (*.example.com), IPv4, and IPv6 addresses
+  const hostRegex =
+    /^(?:\*|\*\.[a-z0-9-]+(?:\.[a-z0-9-]+)*|[a-z0-9-]+(?:\.[a-z0-9-]+)*|\d{1,3}(\.\d{1,3}){3}|([a-fA-F0-9:]+:+)+[a-fA-F0-9]+(?:%[a-zA-Z0-9]+)?)$/;
+  return hostRegex.test(value);
+};