Interceptor (Experimental) para Angular4

token-request-options.service.ts

import {Injectable} from '@angular/core';
import {BaseRequestOptions, RequestOptions} from '@angular/http';

@Injectable()
export class TokenRequestOptionsService extends BaseRequestOptions {
  private token: string;

  constructor() {
    super();
    this.addToken();
  }

  addToken() {
    if (sessionStorage.getItem('token')) {
      this.token = sessionStorage.getItem('token');
      this.headers.set('Authorization', `Bearer ${this.token}`);
    }
  }
}

export const tokenRequestOptionsProvider = { provide: RequestOptions, useClass: TokenRequestOptionsService };