Authorization Token Interceptor Service - Async HTTP Interceptors | Angular 6.x | rxjs 6.x

authorization-token-interceptor.service.ts

import { Injectable } from '@angular/core';
import { HttpErrorResponse, HttpHandler, HttpInterceptor, HttpRequest } from '@angular/common/http';
import { Observable } from 'rxjs';
import { mergeMap } from 'rxjs/operators';
import { User } from 'oidc-client';

import { AuthService } from './oidc-auth.service.ts';

@Injectable({
    providedIn: 'root'
})
export class TokenInterceptor implements HttpInterceptor {

    constructor(private auth: AuthService) { }

    intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        return this.auth.getUser()
            .pipe(
                mergeMap((user: User) => {

                    // OPTIONAL - wrapper to do nothing if pre-flight request
                    if (request.method !== 'OPTIONS') {
                        if (user) {
                            // clone and modify the request
                            request = request.clone({
                                setHeaders: {
                                    'Authorization': `Bearer ${user.access_token}`
                                }
                            });
                        }

                        return next.handle(request)
                            .pipe(
                                tap(
                                    () => {
                                        // OPTIONAL - do something on success
                                    },
                                    (err: any) => {
                                        // handle request errors
                                        if (err instanceof HttpErrorResponse) {
                                            if (err.status === 401) {
                                                // TODO - your choice of UserManager function to renew authorization i.e. singinSilent or signinRedirect.

                                            }
                                        }
                                    }));
                    } else {
                        return next.handle(request);
                    }
                }));
    }
}