Token Interceptor with Storage Service Ionic

token-interceptor.ts

import { Injectable } from '@angular/core';
import {HttpEvent, HttpHandler, HttpInterceptor, HttpRequest} from '@angular/common/http';
import {Observable} from 'rxjs';
import {Storage} from '@ionic/storage';
import { fromPromise } from 'rxjs/observable/fromPromise';
import {flatMap} from 'rxjs/operators';

@Injectable({
  providedIn: 'root'
})
export class TokenInterceptorService implements HttpInterceptor {

  constructor(private storage: Storage) {
  }

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    return fromPromise(this.storage.get('token'))
        .pipe(
            flatMap((token) => {
              const newRequest = req.clone({
                setHeaders: {
                  Authorization: 'Bearer ' + token
                }
              });
              return next.handle(newRequest);
            })
        );
  }
}