Mention OAuth 2 requires RabbitMQ 4.1

Author: acogoluegnes

src/main/java/com/rabbitmq/client/amqp/ConnectionSettings.java

@@ -154,6 +154,14 @@ public interface ConnectionSettings<T> {
    */
   Affinity<? extends T> affinity();
 
+  /**
+   * OAuth 2 settings.
+   *
+   * <p>OAuth 2 requires RabbitMQ 4.1 or more.
+   *
+   * @return OAuth 2 settings
+   * @see OAuth2Settings
+   */
   OAuth2Settings<? extends T> oauth2();
 
   /**

src/main/java/com/rabbitmq/client/amqp/OAuth2Settings.java

@@ -23,6 +23,8 @@
  * Configuration to retrieve a token using the <a
  * href="https://tools.ietf.org/html/rfc6749#section-4.4">OAuth 2 Client Credentials flow</a>.
  *
+ * <p>OAuth 2 requires RabbitMQ 4.1 or more.
+ *
  * @param <T> the type of object returned by methods, usually the object itself
  */
 public interface OAuth2Settings<T> {