Angular Tutorial — Implement Refresh Token with HttpInterceptor

token-interceptor.service.ts

// src/app/services/token-interceptor.service.ts

import { Injectable } from "@angular/core";
import { HttpRequest, HttpHandler, HttpEvent, HttpInterceptor } from "@angular/common/http";
import { AuthenticationService } from "../authentication.service";
import { Observable } from "rxjs/Observable";
import { BehaviorSubject } from "rxjs/BehaviorSubject";

@Injectable()
export class RefreshTokenInterceptor implements HttpInterceptor {
    private refreshTokenInProgress = false;
    // Refresh Token Subject tracks the current token, or is null if no token is currently
    // available (e.g. refresh pending).
    private refreshTokenSubject: BehaviorSubject<any> = new BehaviorSubject<any>(
        null
    );
    constructor(public auth: AuthenticationService) {}

    intercept(
        request: HttpRequest<any>,
        next: HttpHandler
    ): Observable<HttpEvent<any>> {
        return next.handle(request).catch(error => {
            // We don't want to refresh token for some requests like login or refresh token itself
            // So we verify url and we throw an error if it's the case
            if (
                request.url.includes("refreshtoken") ||
                request.url.includes("login")
            ) {
                // We do another check to see if refresh token failed
                // In this case we want to logout user and to redirect it to login page

                if (request.url.includes("refreshtoken")) {
                    this.auth.logout();
                }

                return Observable.throw(error);
            }

            // If error status is different than 401 we want to skip refresh token
            // So we check that and throw the error if it's the case
            if (error.status !== 401) {
                return Observable.throw(error);
            }

            if (this.refreshTokenInProgress) {
                // If refreshTokenInProgress is true, we will wait until refreshTokenSubject has a non-null value
                // – which means the new token is ready and we can retry the request again
                return this.refreshTokenSubject
                    .filter(result => result !== null)
                    .take(1)
                    .switchMap(() => next.handle(this.addAuthenticationToken(request)));
            } else {
                this.refreshTokenInProgress = true;

                // Set the refreshTokenSubject to null so that subsequent API calls will wait until the new token has been retrieved
                this.refreshTokenSubject.next(null);

                // Call auth.refreshAccessToken(this is an Observable that will be returned)
                return this.auth
                    .refreshAccessToken()
                    .switchMap((token: any) => {
                        //When the call to refreshToken completes we reset the refreshTokenInProgress to false
                        // for the next time the token needs to be refreshed
                        this.refreshTokenInProgress = false;
                        this.refreshTokenSubject.next(token);

                        return next.handle(this.addAuthenticationToken(request));
                    })
                    .catch((err: any) => {
                        this.refreshTokenInProgress = false;

                        this.auth.logout();
                        return Observable.throw(error);
                    });
            }
        });
    }

    addAuthenticationToken(request) {
        // Get access token from Local Storage
        const accessToken = this.auth.getAccessToken();

        // If access token is null this means that user is not logged in
        // And we return the original request
        if (!accessToken) {
            return request;
        }

        // We clone the request, because the original request is immutable
        return request.clone({
            setHeaders: {
                Authorization: this.auth.getAccessToken()
            }
        });
    }
}

@cholshwor I think I have your problem before which the refreshAccesssToken() didn't fire HTTP request.
Since I am using Angular 7 with RxJs 6.4, the syntax for the Observable operator is a bit different from above. When I convert the code, I haven't caught the 401 properly. It appears that the refreshAccessToken() didn't fire HTTP request, but in fact, the error returned to the original request subscriber and stopped further processing.

In short, it maybe worth checking whether the 401 is caught.

In RxJs 6.4, my code looks like below:

intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> { // pre request logic return next.handle(requestWithToken(token)).pipe( tap( (event) => { // post request logic }), catchError( ( error ) => { if (error.status == 401) { return refreshTokenRequest().pipe(switchMap((newToken) => next.handle(requestWithToken(newToken))) } return Observable.throw(error); }) }