enable static api url

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
      */