Fix content-type header for external-dns v0.20.0 compatibility

Strip charset parameter from Content-Type header in proxy to match
strict external-dns validation requirements. External-DNS expects
exactly 'application/external.dns.webhook+json;version=1' without
the charset=utf-8 that Express.js adds automatically.

Author: TheOutdoorProgrammer

webhook-proxy/proxy.js

@@ -52,8 +52,16 @@ function proxyRequest(clientReq, clientRes, targetUrl) {
   console.log(`[${clientReq.method}] ${clientReq.url} -> ${url.href}`);
 
   const proxyReq = http.request(options, (proxyRes) => {
-    // Forward status code and headers
-    clientRes.writeHead(proxyRes.statusCode, proxyRes.headers);
+    // Clean up headers - remove charset from content-type for external-dns compatibility
+    const headers = { ...proxyRes.headers };
+    if (headers['content-type']) {
+      // External-DNS expects exactly: application/external.dns.webhook+json;version=1
+      // Express adds charset which breaks strict validation
+      headers['content-type'] = headers['content-type'].replace(/;\s*charset=[^;]+/, '');
+    }
+    
+    // Forward status code and cleaned headers
+    clientRes.writeHead(proxyRes.statusCode, headers);
 
     // Pipe response body
     proxyRes.pipe(clientRes);