add permissive CORS headers

src/server.ts

@@ -12,6 +12,24 @@ import { getIdFilters } from '@welshman/util'
 
 export const server: express.Application = express()
 
+// The browser hits /subscription with an Authorization header and Content-Type:
+// application/json, which triggers a CORS preflight. Answer it and allow the
+// configured origin so the client can register.
+const corsOrigin = process.env.CORS_ORIGIN ?? '*'
+
+server.use((req: Request, res: Response, next: NextFunction) => {
+  res.setHeader('Access-Control-Allow-Origin', corsOrigin)
+  res.setHeader('Access-Control-Allow-Methods', 'GET,POST,DELETE,OPTIONS')
+  res.setHeader('Access-Control-Allow-Headers', 'Content-Type,Authorization')
+  res.setHeader('Access-Control-Max-Age', '86400')
+
+  if (req.method === 'OPTIONS') {
+    return res.sendStatus(204)
+  }
+
+  next()
+})
+
 server.use(express.json())
 
 server.use(express.static('web/dist'))