Clarify wording for the strict REST params message

This commit changes the strict REST parameters message to say that
unconsumed parameters are unrecognized rather than unused. Additionally,
the test is beefed up to include two unused parameters.

Relates #20745

core/src/main/java/org/elasticsearch/rest/BaseRestHandler.java

@@ -30,6 +30,7 @@ import org.elasticsearch.plugins.ActionPlugin;
 import java.io.IOException;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.Set;
 import java.util.stream.Collectors;
 
@@ -63,7 +64,12 @@ public abstract class BaseRestHandler extends AbstractComponent implements RestH
 
         // validate the non-response params
         if (!unconsumedParams.isEmpty()) {
-            throw new IllegalArgumentException("request [" + request.path() + "] contains unused params: " + unconsumedParams.toString());
+            final String message = String.format(
+                Locale.ROOT,
+                "request [%s] contains unrecognized parameters: %s",
+                request.path(),
+                unconsumedParams.toString());
+            throw new IllegalArgumentException(message);
         }
 
         // execute the action

core/src/test/java/org/elasticsearch/rest/BaseRestHandlerTests.java

@@ -33,6 +33,7 @@ import java.util.HashMap;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+import static org.hamcrest.core.AnyOf.anyOf;
 import static org.hamcrest.core.StringContains.containsString;
 import static org.hamcrest.object.HasToString.hasToString;
 import static org.mockito.Mockito.mock;
@@ -51,12 +52,18 @@ public class BaseRestHandlerTests extends ESTestCase {
 
         final HashMap<String, String> params = new HashMap<>();
         params.put("consumed", randomAsciiOfLength(8));
-        params.put("unconsumed", randomAsciiOfLength(8));
+        params.put("unconsumed-first", randomAsciiOfLength(8));
+        params.put("unconsumed-second", randomAsciiOfLength(8));
         RestRequest request = new FakeRestRequest.Builder().withParams(params).build();
         RestChannel channel = new FakeRestChannel(request, randomBoolean(), 1);
         final IllegalArgumentException e =
             expectThrows(IllegalArgumentException.class, () -> handler.handleRequest(request, channel, mock(NodeClient.class)));
-        assertThat(e, hasToString(containsString("request [/] contains unused params: [unconsumed]")));
+        assertThat(
+            e,
+            // we can not rely on ordering of the unconsumed parameters here
+            anyOf(
+                hasToString(containsString("request [/] contains unrecognized parameters: [unconsumed-first, unconsumed-second]")),
+                hasToString(containsString("request [/] contains unrecognized parameters: [unconsumed-second, unconsumed-first]"))));
         assertFalse(executed.get());
     }