title: Angular RxJS sequential requests issue
body: <p>I have the following requests;</p>
  <pre><code>  public userLogin(username: string, password: string) {
      return this.http.post&lt;any&gt;(`${this.apiURL}/login `, {username, password}, constants.httpOptions)
        .pipe(
          map((response) =&gt; {
            this.setToken(response.token);
          })
        );
    }
  
    public getUser() {
      return this.http.get&lt;IUser&gt;(`${this.apiURL}/api/account`)
        .pipe(
          map((user: IUser) =&gt; {
            sessionStorage.setItem('user', JSON.stringify(user));
            this.userSubject.next(user);
          })
        );
    }
  </code></pre>
  <p>I would like to call them sequentially and check the returned value of the last request.
  I implemented the following block of code however, the <code>console.log</code> output is <code>undefined</code> within the <code>subscribe</code> section.
  In the network tab, I can see that both requests are called sequentially and there's no error.</p>
  <pre><code>this.authService.userLogin(username, password).pipe(
          concatMap(() =&gt; { return this.authService.getUser() })
        ).subscribe((res: any) =&gt; {
          console.log(res);
          this.router.navigate(['/home']);
        }, (err: HttpErrorResponse) =&gt; {
          if (err.status === 401) {
            console.log('sign-in page - 401');
            this.unauthorized = true;
          }
        });
  </code></pre>
  <p>What am I doing wrong?</p>