Recommended approach to using an external config file breaks ng add

[fergaldoyle]

The documented approach to fetching config from a file/endpoint (https://github.com/mauriciovigolo/keycloak-angular?tab=readme-ov-file#load-the-keycloak-configuration-using-an-external-file) will break ng add or 'ng update' for any library that needs to modify the ApplicationConfig (to add providers etc) because ng add can no longer parse/understand the source code in main.ts.

e.g. if I have a project using keycloak-angular, fetching a config file then bootstrapping the application, and I try to run ng add @jsverse/transloco I'll get the follow error:
Cannot statically analyze bootstrapApplication call in src/main.ts

I wonder could better support for external config files be added so that we don't have to modify the default bootstrapping code. In CICD pipelines it's pretty common that the application is built/compiled once, and the only thing that changes in DEV/INT/UAT/PREPROD/PROD is a config.json file.

[jcjveraa]

I'd like to second this - we use exactly the same as @fergaldoyle where the config is simply supplied via a well known and controlled backend endpoint (the same backend we need the front end to authenticate to). We serve the frontend with Nginx, which also serves as a reverse proxy for backend calls to the /api endpoint. The frontend simply calls a relative url like GET api/keycloak-config (i.e. on the same host as the frontend is being served from) and this is then proxied to the proper backend which supplies the json.

It would be great if provideKeycloak could natively support an url or a getter-function being passed as the 'config' parameter such that we can leave the appConfig as-is in other respects.

I think ideally the provideKeycloakOptions should have this format:

type ProvideKeycloakOptions = {
  /**
   * Fixed configuration for Keycloak, or a promise that will resolve to a valid config (e.g. an async function that 
   * fetches a valid config from a backend) 
   */
  config: KeycloakConfig | Promise<KeycloakConfig>;

 // etc. as is
};