feat(examples): add authenticated-counter example with verifyJFSRequestBody

examples/authenticated-counter/src/index.ts

@@ -0,0 +1,61 @@
+import { Hono } from "hono";
+import { registerSnapHandler } from "@farcaster/snap-hono";
+import { verifyJFSRequestBody } from "@farcaster/snap";
+import type { SnapHandlerResult } from "@farcaster/snap";
+
+/** In-memory per-FID counter store.
+ * Replace with a real DB (Postgres, Supabase, etc.) in production.
+ */
+const counts = new Map<number, number>();
+
+const app = new Hono();
+
+registerSnapHandler(app, async (ctx): Promise<SnapHandlerResult> => {
+  if (ctx.action.type === "post") {
+    // 1. Verify the POST is genuinely signed by the Farcaster user
+    const verified = await verifyJFSRequestBody(ctx.request);
+    if (!verified) {
+      return {
+        version: "2.0",
+        ui: {
+          root: "page",
+          elements: {
+            page: { type: "stack", props: {}, children: ["err-title", "err-body"] },
+            "err-title": { type: "item", props: { title: "Authentication Failed" } },
+            "err-body": { type: "item", props: { description: "Signature verification failed." } },
+          },
+        },
+      };
+    }
+
+    // 2. Signature verified — safely use the FID
+    const fid = ctx.action.user.fid;
+    counts.set(fid, (counts.get(fid) ?? 0) + 1);
+  }
+
+  const fid = ctx.action.user.fid;
+  const count = counts.get(fid) ?? 0;
+
+  return {
+    version: "2.0",
+    theme: { accent: "green" },
+    ui: {
+      root: "page",
+      elements: {
+        page: { type: "stack", props: {}, children: ["title", "display", "btn"] },
+        title: { type: "item", props: { title: "Authenticated Counter" } },
+        display: {
+          type: "item",
+          props: { description: `FID ${fid} — clicked ${count} time${count === 1 ? "" : "s"}.` },
+        },
+        btn: {
+          type: "button",
+          props: { label: "Increment (+1)" },
+          on: { click: { action: "post" } },
+        },
+      },
+    },
+  };
+});
+
+export default app;