KEYCLOAK-2270 Use sub instead of iss for clientId in JWTClientAuthenticator

integration/adapter-core/src/main/java/org/keycloak/adapters/authentication/JWTClientCredentialsProvider.java

@@ -107,6 +107,7 @@ public class JWTClientCredentialsProvider implements ClientCredentialsProvider {
         JsonWebToken reqToken = new JsonWebToken();
         reqToken.id(AdapterUtils.generateId());
         reqToken.issuer(clientId);
+        reqToken.subject(clientId);
         reqToken.audience(realmInfoUrl);
 
         int now = Time.currentTime();