title: How to correctly chain imported interceptors
body: <p>I am using angular-oauth2-oidc, Angular 7. I believe it imports an interceptor with its import</p>
  
  <pre><code>OAuthModule.forRoot({
         resourceServer: {
           allowedUrls: [environment.backendUrl],
           sendAccessToken: true
         }
       })
  </code></pre>
  
  <p>Additionally I have an interceptor completing an url, which allows me to use only relative paths within httpClient calls of services. e.g.</p>
  
  <pre><code>this.httpClient.get('/resource/' + id)
  </code></pre>
  
  <p>Which is then intercepted to a complete url to the backend</p>
  
  <pre><code>intercept(req: HttpRequest&lt;any&gt;, next: HttpHandler): Observable&lt;HttpEvent&lt;any&gt;&gt; {
          if (!req.url.startsWith('/') || req.url.startsWith('/assets')) {
              return next.handle(req);
          }
  
          const modifiedUrl: string = environment.backendUrl + req.url;
          const modifiedRequest = req.clone({ url: modifiedUrl });
  
          return next.handle(modifiedRequest);
      }
  </code></pre>
  
  <p>Before the url is intercepted the imported Interceptor obviously can't work.</p>
  
  <p>How can I ensure, that the imported interceptor is coming after the own interceptor in chain?</p>
  
  <p>As a temporary solution I added '/' to the allowedUrls, but I don't like this workaround.</p>