Add notification savings + webhook validation

src/lib/neynar.ts

@@ -0,0 +1,34 @@
+const apiKey = process.env.NEYNAR_API_KEY || "";
+
+export async function isSignerValid({
+  fid,
+  signerPublicKey,
+}: {
+  fid: number;
+  signerPublicKey: string;
+}): Promise<boolean> {
+  const url = new URL("https://hub-api.neynar.com/v1/onChainSignersByFid");
+  url.searchParams.append("fid", fid.toString());
+
+  const response = await fetch(url, {
+    method: "GET",
+    headers: {
+      "x-api-key": apiKey,
+    },
+  });
+
+  if (response.status !== 200) {
+    throw new Error(await response.text());
+  }
+
+  const responseJson = await response.json();
+  const signerPublicKeyLC = signerPublicKey.toLowerCase();
+
+  const signerExists = responseJson.events.find(
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    (event: any) =>
+      event.signerEventBody.key.toLowerCase() === signerPublicKeyLC
+  );
+
+  return signerExists;
+}