Set gRPC security interceptor to highest priority

CHANGELOG.md

@@ -5,6 +5,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 ## [Unreleased 3.x]
 ### Added
+- Set gRPC security interceptor to highest priority  ([#5940](https://github.com/opensearch-project/security/pull/5940))
 
 ### Changed
 

src/main/java/org/opensearch/security/filter/SecurityGrpcFilter.java

@@ -69,7 +69,7 @@ public List<OrderedGrpcInterceptor> getOrderedGrpcInterceptors(ThreadContext thr
 
             @Override
             public int order() {
-                return 0;
+                return Integer.MIN_VALUE;
             }
 
             @Override

src/test/java/org/opensearch/security/filter/SecurityGrpcFilterTest.java

@@ -94,4 +94,20 @@ public void testNormalConfigurationReturnsInterceptor() {
             assertTrue(e.getMessage().contains("GuiceHolder") || e instanceof NullPointerException);
         }
     }
+
+    @Test
+    public void testInterceptorOrderIsMinValue() {
+        Settings settings = Settings.builder().put(OpenSearchSecuritySSLPlugin.CLIENT_TYPE, "node").build();
+
+        securityGrpcFilter.initNodeSettings(settings);
+
+        List<GrpcInterceptorProvider.OrderedGrpcInterceptor> interceptors = securityGrpcFilter.getOrderedGrpcInterceptors(threadContext);
+
+        assertEquals("Should return exactly one interceptor", 1, interceptors.size());
+        assertEquals(
+            "Security interceptor should have highest priority (Integer.MIN_VALUE)",
+            Integer.MIN_VALUE,
+            interceptors.get(0).order()
+        );
+    }
 }