Angular 2: custom http service (provider)

import { Injectable } from "@angular/core";
import { Http, Headers, RequestOptions } from '@angular/http';
import { Observable } from 'rxjs/Observable';

@Injectable()

export class CustomHttp { 

  constructor(public http: Http) {

  }
 

  build_headers(): Observable<any> {
    
    return new Observable( (observer) => {

      let headers = new Headers();
      
      headers.append('CONSUMER_SECRET', something_here);
      headers.append('Accept', 'application/json');
      headers.append('Access-Control-Allow-Methods', 'POST');
      headers.append('Content-Type', 'application/json');
      observer.next(new RequestOptions({ 'headers': headers }));
      observer.complete();
    });


  }

  get(url: string): Observable<any> {
    
    return new Observable( observer => {
      this.build_headers().subscribe( (requestOptions: RequestOptions) => {
        this.http.get(url, requestOptions).subscribe( data => {
          observer.next(data);
        }, err => {
          observer.error(err);
        }, () => {
          observer.complete();
        })
      })
    });

  }

  post(url: string, data): Observable<any> {

    return new Observable( observer => {
      this.build_headers().subscribe( (requestOptions: RequestOptions) => {
        this.http.post(url, data, requestOptions).subscribe( data => {
          observer.next(data);
        }, err => {
          observer.error(err);
        }, () => {
          observer.complete();
        })
      })
    });

  }

}