Replacing AtomicReference fields and updating test file

Author: S-Saranya1

core/auth/src/main/java/software/amazon/awssdk/auth/credentials/InstanceProfileCredentialsProvider.java

@@ -27,7 +27,6 @@
 import java.util.Collections;
 import java.util.Map;
 import java.util.Optional;
-import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Supplier;
 import software.amazon.awssdk.annotations.SdkPublicApi;
 import software.amazon.awssdk.annotations.SdkTestInternalApi;
@@ -83,8 +82,10 @@ private enum ApiVersion {
 
     private static final String EC2_METADATA_TOKEN_TTL_HEADER = "x-aws-ec2-metadata-token-ttl-seconds";
     private static final String DEFAULT_TOKEN_TTL = "21600";
-    private final AtomicReference<ApiVersion> apiVersion = new AtomicReference<>(ApiVersion.UNKNOWN);
-    private final AtomicReference<String> resolvedProfile = new AtomicReference<>();
+    
+    // These fields are accessed from methods called by CachedSupplier which provides thread safety through its ReentrantLock
+    private ApiVersion apiVersion = ApiVersion.UNKNOWN;
+    private String resolvedProfile = null;
 
     private final Clock clock;
     private final String endpoint;
@@ -179,7 +180,7 @@ private RefreshResult<AwsCredentials> refreshCredentials() {
         } catch (Ec2MetadataClientException e) {
             if (e.statusCode() == 404) {
                 log.debug(() -> "Resolved profile is no longer available. Resetting it and trying again.");
-                resolvedProfile.set(null);
+                resolvedProfile = null;
                 return refreshCredentials();
             }
             throw SdkClientException.create("Failed to load credentials from IMDS.", e);
@@ -227,7 +228,7 @@ public String toString() {
     }
 
     private String getSecurityCredentialsResource() {
-        return apiVersion.get() == ApiVersion.LEGACY ?
+        return apiVersion == ApiVersion.LEGACY ?
                SECURITY_CREDENTIALS_RESOURCE :
                SECURITY_CREDENTIALS_EXTENDED_RESOURCE;
     }
@@ -310,9 +311,8 @@ private boolean isInsecureFallbackDisabled() {
     }
 
     private String[] getSecurityCredentials(String imdsHostname, String metadataToken) {
-        String profile = resolvedProfile.get();
-        if (profile != null) {
-            return new String[]{profile};
+        if (resolvedProfile != null) {
+            return new String[]{resolvedProfile};
         }
 
         String urlBase = getSecurityCredentialsResource();
@@ -332,12 +332,15 @@ private String[] getSecurityCredentials(String imdsHostname, String metadataToke
                 throw SdkClientException.builder().message("Unable to load credentials path").build();
             }
 
-            apiVersion.compareAndSet(ApiVersion.UNKNOWN, ApiVersion.EXTENDED);
-            resolvedProfile.set(securityCredentials[0]);
+            if (apiVersion == ApiVersion.UNKNOWN) {
+                apiVersion = ApiVersion.EXTENDED;
+            }
+            resolvedProfile = securityCredentials[0];
             return securityCredentials;
 
         } catch (Ec2MetadataClientException e) {
-            if (e.statusCode() == 404 && apiVersion.compareAndSet(ApiVersion.UNKNOWN, ApiVersion.LEGACY)) {
+            if (e.statusCode() == 404 && apiVersion == ApiVersion.UNKNOWN) {
+                apiVersion = ApiVersion.LEGACY;
                 log.debug(() -> "Instance does not support IMDS extended API. Falling back to legacy API.");
                 return getSecurityCredentials(imdsHostname, metadataToken);
             }

core/auth/src/test/java/software/amazon/awssdk/auth/credentials/InstanceProfileCredentialsProviderExtendedApiTest.java

@@ -133,31 +133,6 @@ void resolveCredentials_withImdsDisabled_returnsNoCredentials() {
         verify(0, getRequestedFor(urlPathEqualTo(CREDENTIALS_EXTENDED_RESOURCE_PATH)));
     }
 
-
-    @Test
-    void resolveCredentials_withInvalidProfile_throwsException() {
-        String invalidProfile = "my-profile-0004";
-
-        wireMockServer.stubFor(get(urlPathEqualTo(CREDENTIALS_EXTENDED_RESOURCE_PATH))
-            .willReturn(aResponse().withBody(invalidProfile)));
-        wireMockServer.stubFor(get(urlPathEqualTo(CREDENTIALS_RESOURCE_PATH))
-            .willReturn(aResponse().withBody(invalidProfile)));
-
-        wireMockServer.stubFor(get(urlPathEqualTo(CREDENTIALS_EXTENDED_RESOURCE_PATH + invalidProfile))
-            .willReturn(aResponse().withStatus(404)));
-        wireMockServer.stubFor(get(urlPathEqualTo(CREDENTIALS_RESOURCE_PATH + invalidProfile))
-            .willReturn(aResponse().withStatus(404)));
-
-        wireMockServer.stubFor(put(urlPathEqualTo(TOKEN_RESOURCE_PATH))
-            .willReturn(aResponse().withBody(TOKEN_STUB)));
-
-        InstanceProfileCredentialsProvider provider = InstanceProfileCredentialsProvider.builder().build();
-
-        assertThatThrownBy(() -> provider.resolveCredentials())
-            .isInstanceOf(SdkClientException.class)
-            .hasMessageContaining("Failed to load credentials from IMDS.");
-    }
-
     @Test
     void resolveCredentials_cachesProfile_maintainsAccountId() {
         String credentialsWithAccountId = String.format(