code: public Map<String, String> fetchTokenKeys() {
  		try {
  			return extractTokenKeys(this.restTemplate
  					.getForObject(getUaaUrl() + "/token_keys", Map.class));
  		}
  		catch (HttpStatusCodeException ex) {
  			throw new CloudFoundryAuthorizationException(Reason.SERVICE_UNAVAILABLE,
  					"UAA not reachable");
  		}
  	}
docs: Return all token keys known by the UAA.
  @return a list of token keys