feat(admission): add group VPN exceptions

apps/web/src/lib/admission-settings.ts

@@ -0,0 +1,37 @@
+export interface AdmissionMessages {
+  registrationMessage: string;
+  groupAccessDeniedMessage: string;
+  vpnDeniedMessage: string;
+}
+
+export const DEFAULT_ADMISSION_MESSAGES: AdmissionMessages = {
+  registrationMessage: "Please register your Minecraft account before joining.",
+  groupAccessDeniedMessage: "Your account group does not currently have server access. Contact a host if you believe this is a mistake.",
+  vpnDeniedMessage: "VPN, proxy, and Tor connections are not allowed. Contact a host to request an exception.",
+} as const;
+
+export function admissionDenialMessage(
+  reason: "not_registered" | "group_access_disabled" | "anonymized_network_disallowed",
+  messages: AdmissionMessages,
+) {
+  if (reason === "not_registered") return messages.registrationMessage;
+  if (reason === "group_access_disabled") return messages.groupAccessDeniedMessage;
+  return messages.vpnDeniedMessage;
+}
+
+const CONTROL_CHARACTERS = /[\u0000-\u001f\u007f]/;
+
+function messageValue(formData: FormData, name: string) {
+  const value = String(formData.get(name) ?? "").trim();
+  return value.length >= 10 && value.length <= 500 && !CONTROL_CHARACTERS.test(value)
+    ? value
+    : null;
+}
+
+export function parseAdmissionMessages(formData: FormData) {
+  const registrationMessage = messageValue(formData, "registrationMessage");
+  const groupAccessDeniedMessage = messageValue(formData, "groupAccessDeniedMessage");
+  const vpnDeniedMessage = messageValue(formData, "vpnDeniedMessage");
+  if (!registrationMessage || !groupAccessDeniedMessage || !vpnDeniedMessage) return null;
+  return { registrationMessage, groupAccessDeniedMessage, vpnDeniedMessage };
+}