Merge pull request #30853 from amintong/fix_proxy

fix(proxy-backend): correct rewrite rule to avoid extra subpath

.changeset/late-squids-feel.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-proxy-backend': patch
+---
+
+correct rewrite rule to avoid extra subpath in proxy path

plugins/proxy-backend/src/service/router.ts

@@ -292,8 +292,7 @@ export async function createRouter(
     logger: options.logger,
   };
 
-  const externalUrl = await options.discovery.getExternalBaseUrl('proxy');
-  const { pathname: pathPrefix } = new URL(externalUrl);
+  const pathPrefix = '/api/proxy';
 
   const proxyConfig: ProxyConfig = {
     ...(options.additionalEndpoints ?? {}),