auth.service.ts

import { Injectable } from '@angular/core'
import { HttpClient, HttpErrorResponse } from '@angular/common/http'
import { tap, catchError } from 'rxjs/operators'
import { throwError } from 'rxjs'

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

  constructor(private http: HttpClient) { }

  login(credentials) {
    return this.http.post('/api/authentication', credentials)
      .pipe(
        catchError(this.handleError),
        tap(response => {
          localStorage.setItem('token', response['token'])
        })
      )
  }

  private handleError(error: HttpErrorResponse) {
    if (error.error instanceof ErrorEvent) {
      // Client-side or network error
    } else {
      // Unsuccessful response code
      if (error.status === 401) {
        return throwError( 'Unauthorized.' )
      }
    }
    return throwError( error.error )
  }
}