Fix FIPS configuration handling (#3501)

Fix bug in FIPS configuration handling where setting a non-FIPS region clears
the setting.

Author: dagnir

.changes/next-release/bugfix-WSSDKforJavav2-fface60.json

@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "WS SDK for Java v2",
+    "contributor": "",
+    "description": "Fix bug in FIPS configuration handling where setting a non-FIPS region clears the setting."
+}

core/aws-core/src/main/java/software/amazon/awssdk/awscore/client/builder/AwsDefaultClientBuilder.java

@@ -294,7 +294,7 @@ private DefaultsMode resolveDefaultsMode(SdkClientConfiguration config) {
             defaultsMode = autoDefaultsModeDiscovery.discover(config.option(AwsClientOption.AWS_REGION));
             DefaultsMode finalDefaultsMode = defaultsMode;
             log.debug(() -> String.format("Resolved %s client's AUTO configuration mode to %s", serviceName(),
-                      finalDefaultsMode));
+                                          finalDefaultsMode));
         }
 
         return defaultsMode;
@@ -389,7 +389,9 @@ public final BuilderT region(Region region) {
         }
 
         clientConfiguration.option(AwsClientOption.AWS_REGION, regionToSet);
-        clientConfiguration.option(AwsClientOption.FIPS_ENDPOINT_ENABLED, fipsEnabled);
+        if (fipsEnabled != null) {
+            clientConfiguration.option(AwsClientOption.FIPS_ENDPOINT_ENABLED, fipsEnabled);
+        }
         return thisBuilder();
     }
 

core/aws-core/src/test/java/software/amazon/awssdk/awscore/client/builder/DefaultAwsClientBuilderTest.java

@@ -105,14 +105,25 @@ public void buildWithRegionShouldHaveCorrectEndpointAndSigningRegion() {
     }
 
     @Test
-    public void buildWithFipsRegionThenNonFipsFipsEnabledFlagUnset() {
+    public void buildWithFipsRegionThenNonFipsFipsEnabledRemainsSet() {
         TestClient client = testClientBuilder()
             .region(Region.of("us-west-2-fips")) // first call to setter sets the flag
             .region(Region.of("us-west-2"))// second call should clear
             .build();
 
         assertThat(client.clientConfiguration.option(AwsClientOption.AWS_REGION)).isEqualTo(Region.US_WEST_2);
-        assertThat(client.clientConfiguration.option(AwsClientOption.FIPS_ENDPOINT_ENABLED)).isNull();
+        assertThat(client.clientConfiguration.option(AwsClientOption.FIPS_ENDPOINT_ENABLED)).isTrue();
+    }
+
+    @Test
+    public void buildWithSetFipsTrueAndNonFipsRegionFipsEnabledRemainsSet() {
+        TestClient client = testClientBuilder()
+            .fipsEnabled(true)
+            .region(Region.of("us-west-2"))
+            .build();
+
+        assertThat(client.clientConfiguration.option(AwsClientOption.AWS_REGION)).isEqualTo(Region.US_WEST_2);
+        assertThat(client.clientConfiguration.option(AwsClientOption.FIPS_ENDPOINT_ENABLED)).isTrue();
     }
 
     @Test