Reapply "enable static api url"

This reverts commit beffae47af.

apps/login/next-env-vars.d.ts

@@ -10,10 +10,18 @@ declare namespace NodeJS {
     SYSTEM_USER_PRIVATE_KEY: string; // The fallback service user private key
 
     /**
-     * Self hosting: The instance url
+     * Self hosting: The Zitadel API url
      */
     ZITADEL_API_URL: string;
 
+    /**
+     * Takes effect only if ZITADEL_API_URL is not empty.
+     * This is only relevant if Zitadels runtime has the ZITADEL_INSTANCEHOSTHEADERS config changed.
+     * The default is x-zitadel-instance-host.
+     * Most users don't need to set this variable.
+     */
+    ZITADEL_INSTANCE_HOST_HEADER: string
+
     /**
      * Self hosting: The service user id
      */

apps/login/src/lib/service.ts

@@ -42,8 +42,15 @@ export async function createServiceForHost<T extends ServiceClass>(
     throw new Error("No token found");
   }
 
+  const instanceHost = new URL(serviceUrl).host
   const transport = createServerTransport(token, {
-    baseUrl: serviceUrl,
+    baseUrl: process.env.ZITADEL_API_URL ?? serviceUrl,
+    interceptors: process.env.ZITADEL_API_URL && process.env.ZITADEL_API_URL != serviceUrl || process.env.ZITADEL_INSTANCE_HOST_HEADER ? [(next) => {
+      return (req) => {
+        req.header.set(process.env.ZITADEL_INSTANCE_HOST_HEADER ?? "x-zitadel-instance-host", instanceHost)
+        return next(req)
+      }
+    }] : undefined
   });
 
   return createClientFor<T>(service)(transport);

turbo.json

@@ -12,7 +12,8 @@
     "ZITADEL_API_URL",
     "ZITADEL_SERVICE_USER_ID",
     "ZITADEL_SERVICE_USER_TOKEN",
-    "NEXT_PUBLIC_BASE_PATH"
+    "NEXT_PUBLIC_BASE_PATH",
+    "ZITADEL_INSTANCE_HOST_HEADER"
   ],
   "tasks": {
     "generate": {