Unable to access application context in discovery

[trajano]

Describe the bug
Though I fixed the documentation in #2733 I am still unable to use the rate limiter in Discovery. It appears that in the code you're assembling a new evaluation context containing only the metadata and not include the rest of the context so defining a keyresolver does not work inside discovery

In DiscoveryClientRouteDefinitionLocator specifically

	private DiscoveryClientRouteDefinitionLocator(String discoveryClientName, DiscoveryLocatorProperties properties) {
		this.properties = properties;
		if (StringUtils.hasText(properties.getRouteIdPrefix())) {
			routeIdPrefix = properties.getRouteIdPrefix();
		}
		else {
			routeIdPrefix = discoveryClientName + "_";
		}
               // context is built here
		evalCtxt = SimpleEvaluationContext.forReadOnlyDataBinding().withInstanceMethods().build();
	}

// and only gets the info from the service instance.

	String getValueFromExpr(SimpleEvaluationContext evalCtxt, SpelExpressionParser parser, ServiceInstance instance,
			Map.Entry<String, String> entry) {
		try {
			Expression valueExpr = parser.parseExpression(entry.getValue());
			return valueExpr.getValue(evalCtxt, instance, String.class);
		}
		catch (ParseException | EvaluationException e) {
			if (log.isDebugEnabled()) {
				log.debug("Unable to parse " + entry.getValue(), e);
			}
			throw e;
		}
	}

Sample
If possible, please provide a test case or sample application that reproduces
the problem. This makes it much easier for us to diagnose the problem and to verify that
we have fixed it.

[trajano]

I'm trying a workaround which is to create a custom filter factory like this

@Component
public class DiscoveryRequestRateLimiterGatewayFilterFactory
    extends RequestRateLimiterGatewayFilterFactory {

  public DiscoveryRequestRateLimiterGatewayFilterFactory(
      RateLimiter defaultRateLimiter,
      @Qualifier("tokenKeyResolver") KeyResolver defaultKeyResolver) {

    super(defaultRateLimiter, defaultKeyResolver);
  }
}

[spencergibb]

This has been restricted for security. See c76b775

We could add something similar for DiscoveryClientRouteDefinitionLocator