Append header to all Http Requests -> Angular2

You can override Angular's Http class, add headers there and then provide CustomHttp class in your modules:

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Rx';
import { RequestOptionsArgs, RequestOptions, ConnectionBackend, Http, Request, Response, Headers } from "@angular/http";

@Injectable()
export class CustomHttp extends Http {

headers: Headers = new Headers({ 'Something': 'Something' });
options1: RequestOptions = new RequestOptions({ headers: this.headers });

constructor(backend: ConnectionBackend,
    defaultOptions: RequestOptions) {
    super(backend, defaultOptions);
}

get(url: string, options?: RequestOptionsArgs) {
    console.log('Custom get...');
    return super.get(url, this.options1).catch(err => {
        console.log(err);
    });
}
}

You need to do the same for post, put, delete etc. And in your module:

{ provide: Http, 
    useFactory: (
        backend: XHRBackend,
        defaultOptions: RequestOptions) =>
        new CustomHttp(backend, defaultOptions),
    deps: [XHRBackend, RequestOptions]
}