Add guide note

Signed-off-by: Thomas Farr <[email protected]>

guides/auth.md

@@ -7,14 +7,19 @@
 
 Requests to [OpenSearch Service and OpenSearch Serverless](https://docs.aws.amazon.com/opensearch-service/index.html) must be signed using the AWS signing protocol. Use `AwsSdk2Transport` to send signed requests.
 
+> ⚠️ **Warning** ⚠️  
+> Using `software.amazon.awssdk.http.apache.ApacheHttpClient` is discouraged as it does not support request bodies on GET or DELETE requests.  
+> This leads to incorrect handling of requests such as `OpenSearchClient.clearScroll()` and `OpenSearchClient.deletePit()`.  
+> As such `AwsSdk2Transport` will throw a `TransportException` if an unsupported request is encountered while using `ApacheHttpClient`.
+
 ```java
-SdkHttpClient httpClient = ApacheHttpClient.builder().build();
+SdkHttpClient httpClient = AwsCrtHttpClient.builder().build();
 
 OpenSearchClient client = new OpenSearchClient(
     new AwsSdk2Transport(
         httpClient,
         "search-...us-west-2.es.amazonaws.com", // OpenSearch endpoint, without https://
-        "es" // signing service name, use "aoss" for OpenSearch Serverless
+        "es", // signing service name, use "aoss" for OpenSearch Serverless
         Region.US_WEST_2, // signing service region
         AwsSdk2TransportOptions.builder().build()
     )