app.module.ts

@NgModule({
  imports: [OAuthModule.forRoot({...})] // <-- how to use the configuration.json here
})
export class AppModule {
  constructor(@Inject(AppConfig) private readonly appConfig: AppConfiguration) {} // I can inject
}

configuration.json

{
  "apiBaseUrl": "https://localhost:5301"
}

configuration.ts

export interface AppConfiguration {
  apiBaseUrl: string;
}

export const AppConfig = new InjectionToken<AppConfiguration>('@@appConfiguration');

main.ts

(async () => {
  try {
    const config: AppConfiguration = await fetch('assets/configuration.json').then(res => res.json());

    if (config.production) {
      console.log('Running in production mode');
      enableProdMode();
    }

    platformBrowserDynamic([
      { provide: AppConfig, useValue: config }
    ]).bootstrapModule(AppModule)
      .catch(err => console.error(err));

  } catch (e) {
    console.error('Error initializing', e);
  }
})()