Add map import and export with durable refresh progress

lib/map-archive-signature.ts

@@ -0,0 +1,23 @@
+import { createHmac, timingSafeEqual } from "node:crypto";
+import {
+  archiveMetadataSchema,
+  type ArchiveMetadata,
+} from "../shared/map-archive";
+
+export function archiveSignature(value: ArchiveMetadata, key: string) {
+  const { signature: _signature, ...metadata } =
+    archiveMetadataSchema.strip().parse(value);
+  return createHmac("sha256", key)
+    .update("minegeo-map-share/v1\n")
+    .update(JSON.stringify(metadata))
+    .digest("hex");
+}
+export function verifyArchiveSignature(value: ArchiveMetadata, key: string) {
+  const expected = Buffer.from(archiveSignature(value, key), "hex");
+  const supplied = Buffer.from(value.signature, "hex");
+  if (
+    expected.length !== supplied.length ||
+    !timingSafeEqual(expected, supplied)
+  )
+    throw new Error("Map ZIP ownership verification failed");
+}