Modifying Http Requests with Interceptors in Angular

auth.interceptor.ts

import {HttpEvent, HttpHandler, HttpInterceptor, HttpRequest} from '@angular/common/http';
import {Observable} from 'rxjs/Observable';

export class AuthInterceptor implements HttpInterceptor {
  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    const reqCopied = req.clone({
      headers: req.headers.append('', ''),
      params: req.params.set('', '')
    });
    return next.handle(reqCopied);
  }
}

app.module.ts

import {BrowserModule} from '@angular/platform-browser';
import {NgModule} from '@angular/core';
import {FormsModule} from '@angular/forms';

import {AppComponent} from './app.component';
import {HTTP_INTERCEPTORS, HttpClientModule} from '@angular/common/http';
import {AuthInterceptor} from './auth.interceptor';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    FormsModule,
    HttpClientModule
  ],
  providers: [
    {provide: HTTP_INTERCEPTORS, useClass: AuthInterceptor, multi: true}
  ],
  bootstrap: [AppComponent]
})
export class AppModule {
}

References
https://angular.io/guide/http#intercepting-requests-and-responses

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