feat: add onboarding with oldmarr import (#1606)

packages/old-import/src/import/validate-token.ts

@@ -0,0 +1,18 @@
+import { decryptSecretWithKey } from "@homarr/common/server";
+
+export const ensureValidTokenOrThrow = (checksum: string | undefined, encryptionToken: string | null) => {
+  if (!encryptionToken || !checksum) return;
+
+  const [first, second] = checksum.split("\n");
+  if (!first || !second) throw new Error("Malformed checksum");
+
+  const key = Buffer.from(encryptionToken, "hex");
+  let decrypted: string;
+  try {
+    decrypted = decryptSecretWithKey(second as `${string}.${string}`, key);
+  } catch {
+    throw new Error("Invalid checksum");
+  }
+  const isValid = decrypted === first;
+  if (!isValid) throw new Error("Invalid checksum");
+};