Initial work, copied from the Shopify provider

framework/saleor/api/utils/is-allowed-method.ts

@@ -0,0 +1,28 @@
+import type { NextApiRequest, NextApiResponse } from 'next'
+
+export default function isAllowedMethod(
+  req: NextApiRequest,
+  res: NextApiResponse,
+  allowedMethods: string[]
+) {
+  const methods = allowedMethods.includes('OPTIONS')
+    ? allowedMethods
+    : [...allowedMethods, 'OPTIONS']
+
+  if (!req.method || !methods.includes(req.method)) {
+    res.status(405)
+    res.setHeader('Allow', methods.join(', '))
+    res.end()
+    return false
+  }
+
+  if (req.method === 'OPTIONS') {
+    res.status(200)
+    res.setHeader('Allow', methods.join(', '))
+    res.setHeader('Content-Length', '0')
+    res.end()
+    return false
+  }
+
+  return true
+}