Get external configuration file before bootstrap in Angular 2. See also https://blog.sstorie.com/providing-external-data-when-bootstrapping-angular-2/

main.ts

import { bootstrap          } from '@angular/platform-browser-dynamic';
import { HTTP_PROVIDERS     } from '@angular/http';
import { Http, 
         Request,
         Response,
         XSRFStrategy,
         CookieXSRFStrategy } from '@angular/http';
import { Injector,
         ReflectiveInjector } from '@angular/core';
import { Observable         } from 'rxjs/Rx';

import { Configuration      } from './config/configuration';
import { AppComponent       } from './app.component';

export function configureAndRunApplication(configUrl: string) {

  let http: Http = getHttp();

  getConfig(http)
    .then((json: string) => {
      let configuration: Configuration = Configuration.fromJson(json);
      
      bootstrap(AppComponent, [
        HTTP_PROVIDERS,
        { provide: 'app.config', useValue: configuration }
      ]);
    }, handleError);
  
  function getConfig(http: Http): Promise<string> {
    return http.get(configUrl)
      .map((response: Response) => {
        return response.text();
      })
      .catch(handleError)
      .toPromise();
  }
  
  function getHttp(): Http {
    let injector: Injector = ReflectiveInjector.resolveAndCreate([
      ...HTTP_PROVIDERS,
      { provide: XSRFStrategy, useValue: new NoCheckCookieXSRFStrategy() }
    ]);
    return injector.get(Http);
  }
  
  function handleError(error: any) {
    let errMsg = (error.message) ? error.message :
      error.status ? `${error.status} - ${error.statusText}` : 'Server error';
      console.error(errMsg);
    return Observable.throw(errMsg);
  }
}

/**
 * This is required as we are not using the platform brower. The original
 * CookieXSRFStrategy would call the platform browser to get the cookies.
 * We don't need it here, as we are just making a simple GET request
 * to get the configuration file. The main application will not be using
 * this or the custom made `Http` object.
 */
class NoCheckCookieXSRFStrategy extends CookieXSRFStrategy {
  
  configureRequest(request: Request) {
    // noop
  }
}

Update for newer Angular http://stackoverflow.com/a/39454713/2587435