fix(@angular/ssr): support custom headers in redirect responses

Updates createRedirectResponse to accept an optional Record<string, string> of headers, allowing custom headers to be merged into the redirect response. The Location and Vary: X-Forwarded-Prefix headers are automatically set to ensure correct routing and proxy behavior.

AngularServerApp now passes relevant headers from the matched route or response context when creating a redirect.

Author: alan-agius4

packages/angular/ssr/src/app.ts

@@ -190,7 +190,7 @@ export class AngularServerApp {
       return null;
     }
 
-    const { redirectTo, status, renderMode } = matchedRoute;
+    const { redirectTo, status, renderMode, headers } = matchedRoute;
 
     if (redirectTo !== undefined) {
       return createRedirectResponse(
@@ -199,6 +199,7 @@ export class AngularServerApp {
           buildPathWithParams(redirectTo, url.pathname),
         ),
         status,
+        headers,
       );
     }
 
@@ -352,7 +353,7 @@ export class AngularServerApp {
     }
 
     if (result.redirectTo) {
-      return createRedirectResponse(result.redirectTo, responseInit.status);
+      return createRedirectResponse(result.redirectTo, responseInit.status, headers);
     }
 
     if (renderMode === RenderMode.Prerender) {

packages/angular/ssr/src/utils/redirect.ts

@@ -27,9 +27,14 @@ export function isValidRedirectResponseCode(code: number): boolean {
  * @param location - The URL to which the response should redirect.
  * @param status - The HTTP status code for the redirection. Defaults to 302 (Found).
  *                 See: https://developer.mozilla.org/en-US/docs/Web/API/Response/redirect_static#status
+ * @param headers - Additional headers to include in the response.
  * @returns A `Response` object representing the HTTP redirect.
  */
-export function createRedirectResponse(location: string, status = 302): Response {
+export function createRedirectResponse(
+  location: string,
+  status = 302,
+  headers?: Record<string, string>,
+): Response {
   if (ngDevMode && !isValidRedirectResponseCode(status)) {
     throw new Error(
       `Invalid redirect status code: ${status}. ` +
@@ -40,7 +45,9 @@ export function createRedirectResponse(location: string, status = 302): Response
   return new Response(null, {
     status,
     headers: {
+      ...headers,
       'Location': location,
+      'Vary': 'X-Forwarded-Prefix',
     },
   });
 }