[User Authentication Using Google OAuth 2.0 APIs for TVs & Devices] This is an Angular service that invokes the Google APIs to authenticate a user in an app that doesn't run on a browser, for e.g. a desktop app. This service uses RxJS to retry the REST API calls at a specific interval in case of failure due to unstable internet connection. #Angu…

google-device-auth.service.ts

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { retryWhen, delay, tap, scan, concatMap } from 'rxjs/operators';

@Injectable({
  providedIn: 'root'
})
export class GoogleDeviceAuthService {

  private readonly client_id = "<client-id>";
  private readonly client_secret = "<client-secret>";

  private readonly userCodeRequest = {
    "client_id": this.client_id,
    "scope": "email profile"
  };

  private readonly pollGoogleAuthServerRequestTemplate = {
    "client_id": this.client_id,
    "client_secret": this.client_secret,
    "code": "",
    "grant_type": "http://oauth.net/grant_type/device/1.0"
  }

  private readonly userCodeUrl = "https://accounts.google.com/o/oauth2/device/code";

  private readonly pollGoogleAuthServerUrl = "https://www.googleapis.com/oauth2/v4/token";

  constructor(private readonly http: HttpClient) { }

  public getUserCode() {
    return this.http.post(this.userCodeUrl, this.userCodeRequest)
      .pipe(
        retryWhen(err => err.pipe(
          scan(
            (retryCount, err) => {
              if (retryCount > 3)
                throw err;
              else
                return retryCount + 1;
            }, 0
          ),
          delay(1000),
          tap(err => console.log("Retrying...", err))
        )));
  }

  public checkAuthServerForUserInput(deviceCode) {
    let pollGoogleAuthServerRequest = { ...this.pollGoogleAuthServerRequestTemplate, ...{ "code": deviceCode } };
    return this.http.post(this.pollGoogleAuthServerUrl, pollGoogleAuthServerRequest)
      .pipe(
        retryWhen(err => err.pipe(
          scan(
            (retryCount, err) => {
              if (retryCount > 3)
                throw err;
              else
                return retryCount + 1;
            }, 0
          ),
          delay(1000),
          tap(err => console.log("Retrying...", err))
        )));;
  }
}