fix(proxy-backend): correct rewrite rule to avoid extra subpath in proxy path\n\nUse getBaseUrl instead of getExternalBaseUrl for pathPrefix, ensuring rewrite rule is /api/proxy/... and not /subpach/api/proxy/...\n\nAdded changeset for patch release.

Signed-off-by: amintong <amintong@tencent.com>

.changeset/late-squids-feel.md

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

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

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