Http interceptor for ionic 3, this allow us to make actions like obtain a JWT token before send the request. Sample of implementation at http://ldmarz.com/ionic3-http-interceptor/

http-interceptor.ts

import {Http, RequestOptionsArgs, Response, RequestOptions, ConnectionBackend, Headers} from '@angular/http';
import 'rxjs/add/operator/map';
import { Observable } from 'rxjs/Observable';
import { Storage } from '@ionic/storage';

export class HttpProvider extends Http {
  
  constructor (connectionBackend: ConnectionBackend, requestOptions: RequestOptions, public storage: Storage ) {
    super(connectionBackend, requestOptions);
  }

  get(url: string, options?: RequestOptionsArgs): Observable<Response> {
    return Observable.fromPromise (
      this.getRequestOptionArgs()
    ).mergeMap((options) => { return super.get(url, options) });
  }

  post(url: string, body: string, options?: RequestOptionsArgs): Observable<Response> {   
    return Observable.fromPromise (
      this.getRequestOptionArgs()
    ).mergeMap((options) => { return super.post(url, body, options) })
  }

  put(url: string, body: string, options?: RequestOptionsArgs): Observable<Response> {
    return Observable.fromPromise (
      this.getRequestOptionArgs()
    ).mergeMap((options) => { return super.put(url, body, options) })
  }

  getRequestOptionArgs(options?: RequestOptionsArgs) {
    return this.storage.get('token')
    .then((token) => {
      if (options == null) {
        options = new RequestOptions();
      }
      if (options.headers == null) {
          options.headers = new Headers();
      }
      if (token !== null) {
        options.headers.append('Authorization','Bearer ' + token);  
      }
      options.headers.append('Content-Type', 'application/json');

      return options;  
    })
  }
}

Hi there, Thanks for this very useful code. Can you help me add a piece to it to support refresh tokens?
I have been trying for two days and I have been stuck.
Look here please: https://stackoverflow.com/questions/45655939/ionic-storage-get-returns-null-only-on-the-second-call-within-method