Fix client credentials grant token invalidation

- Fixes gh-1335
- Cherry-picked from 5.x.x branch (6c81106)

Signed-off-by: Daniel Garnier-Moiroux <daniel.garnier-moiroux@broadcom.com>

Author: Kehrlann

cloudfoundry-client-reactor/src/main/java/org/cloudfoundry/reactor/tokenprovider/AbstractUaaTokenProvider.java

@@ -74,7 +74,7 @@ public abstract class AbstractUaaTokenProvider implements TokenProvider {
 
     private static final ZoneId UTC = ZoneId.of("UTC");
 
-    private final ConcurrentMap<ConnectionContext, Mono<String>> accessTokens =
+    protected final ConcurrentMap<ConnectionContext, Mono<String>> accessTokens =
             new ConcurrentHashMap<>(1);
 
     private final ConcurrentMap<ConnectionContext, RefreshToken> refreshTokenStreams =

cloudfoundry-client-reactor/src/main/java/org/cloudfoundry/reactor/tokenprovider/_ClientCredentialsGrantTokenProvider.java

@@ -16,6 +16,7 @@
 
 package org.cloudfoundry.reactor.tokenprovider;
 
+import org.cloudfoundry.reactor.ConnectionContext;
 import org.cloudfoundry.reactor.TokenProvider;
 import org.immutables.value.Value;
 import reactor.netty.http.client.HttpClientForm;
@@ -36,4 +37,9 @@ void tokenRequestTransformer(HttpClientRequest request, HttpClientForm form) {
             .attr("response_type", "token");
     }
 
+    @Override
+    public void invalidate(ConnectionContext connectionContext) {
+        this.accessTokens.remove(connectionContext);
+    }
+
 }