app.url.ts

export const GAME_FORMAT = '/#{sessionId}/game/format';

game-web-app-page.ts

@Component(...)
export class ProfilePage {
   ...
   
   async getGameApp() {
     try {
       const userId = await this.userService.getUserId();
       const userIdToken = userId?.token || '';
       this.gameService.formatUserIdToken(userIdToken).subscribe((formattedId) => {
         const url = [ENV.GAME_WEB_APP_URL, `formattedId=${formattedId}`].join('?');
         Browser.open(url);
       });
     } catch (err) {
       this.errorService.reportError(err);
     }
   }
}

game-web-service.ts

export class GameService {
   ...

   async formatUserId(userIdToken: String) {
     return from(this.http.get(
       this.urlBuilder.build(GAME_FORMAT, {
         sessionId: this.sessionId,
       }, {
         queryParams: { userIdToken },
       })
     )).pipe(
       map(({ body: { formattedId } }): FormatUserIdResponse) => formattedId),
       throwIfEmpty(() => new Error('Failed to format token'),
       catchError((e) => {
         return of(e);
       })
     );
   }
}