Create constants file for identity constants

Signed-off-by: Craig Perkins <[email protected]>

server/src/main/java/org/opensearch/identity/IdentityConstants.java

@@ -0,0 +1,18 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.identity;
+
+/**
+ * Class containing constants used in the identity module
+ *
+ * @opensearch.experimental
+ */
+public class IdentityConstants {
+    public static final String SUBJECT_TRANSIENT_NAME = "subject.name";
+}

server/src/main/java/org/opensearch/identity/RunAsSubjectClient.java

@@ -19,6 +19,8 @@
 import org.opensearch.core.action.ActionListener;
 import org.opensearch.core.action.ActionResponse;
 
+import static org.opensearch.identity.IdentityConstants.SUBJECT_TRANSIENT_NAME;
+
 /**
  * Implementation of client that will run transport actions in a stashed context and inject the name of the provided
  * subject into the context.
@@ -30,8 +32,6 @@ public class RunAsSubjectClient extends FilterClient {
 
     private static final Logger logger = LogManager.getLogger(RunAsSubjectClient.class);
 
-    public static final String SUBJECT_TRANSIENT_NAME = "subject.name";
-
     private final Subject subject;
 
     public RunAsSubjectClient(Client delegate, Subject subject) {