Add HMAC function, and update the CMS and Mailer services

A new module has been added to create HMACs, primarily used in the billing service for data verification. Keystatic CMS usage has been conditioned to Node.js runtime only, and a fallback to the mock CMS client has been implemented for Edge Runtime. Mailer services now accommodate environment-specific providers.

packages/billing/lemon-squeezy/src/services/verify-hmac.ts

@@ -0,0 +1,33 @@
+function bufferToHex(buffer: ArrayBuffer) {
+  return Array.from(new Uint8Array(buffer))
+    .map((b) => b.toString(16).padStart(2, '0'))
+    .join('');
+}
+
+export async function createHmac({ key, data }: { key: string; data: string }) {
+  const encoder = new TextEncoder();
+  const crypto = new Crypto();
+  const encodedKey = encoder.encode(key);
+  const encodedData = encoder.encode(data);
+
+  const hmacKey = await crypto.subtle.importKey(
+    'raw',
+    encodedKey,
+    {
+      name: 'HMAC',
+      hash: 'SHA-256',
+    },
+    true,
+    ['sign', 'verify'],
+  );
+
+  const signature = await window.crypto.subtle.sign(
+    'HMAC',
+    hmacKey,
+    encodedData,
+  );
+
+  const hex = bufferToHex(signature);
+
+  return { hex };
+}