Effective & Secure Method to populate Access Token for authorization header in Rest Template

Question

I am trying to consume a REST endpoint by using the RestTemplate Library provided by the spring framework. The endpoint also demands a Bearer Access Token as its authorization header, which is only obtained as the response from a user authentication endpoint, which in turn expects an encoded Basic Auth in its Header.

This is the high-level implementation that I have done thus far.

HttpHeaders headers = new HttpHeaders();
    headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));
    headers.setBearerAuth(fetchAccessToken());
    HttpEntity<String> entity = new HttpEntity<String>("parameters",headers);
    ResponseEntity<?> result = this.restClient.exchange(urlToConsume, HttpMethod.GET, entity, String.class);

The 'fetchAccessToken' Method is implemented as follows

HttpHeaders headers = new HttpHeaders();
    headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));
    headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
    headers.setBasicAuth(externalDestination.getClientId(),
            externalDestination.getClientSecret());
    HttpEntity<String> entity = new HttpEntity<String>("parameters", headers);

    ResponseEntity<?> result = restClient.exchange(authUrl, HttpMethod.GET, entity, String.class);
    //And Thereby fetching 'access_token' from the successful fetch.

I Want to know whether there is any cleaner way to replicate the above task of dealing with multiple Rest calls to accomplish a single task. Also, I want to know whether I am missing out any essential validations from a security point of view.

Answer 1

You can have an interceptor on RestTemplate. It will be called for each request. You can have the access token logic within the interceptor. You can also implementing caching so that you do not fire two requests for each task. In case the token expires (401 response), you can regenerate the token

@Component
class MyInterceptor implements ClientHttpRequestInterceptor {
   @Override
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution){
      HttpHeaders headers = request.getHeaders();
      headers.setBearerAuth(someCachedService.getBearerToken());
      ... response = execution.execute(request, body);
     // handle unauthorized request

   }
}

@Bean
RestTemplate restTemplate(MyInterceptor interceptor){
  RestTemplate restTemplate = new RestTemplate();
  restTemplate.setInterceptors(Arrays.asList(interceptor));
}