[AI-FSSDK] [FSSDK-12273] Add support for customHeaders option for polling datafile manager

- Added withCustomHeaders(Map<String, String>) builder method to HttpProjectConfigManager
- Custom headers are applied after SDK headers to allow user override
- Implemented immutable copy of headers for thread safety
- Added 7 comprehensive unit tests covering:
  * Custom headers included in HTTP requests
  * Custom headers override SDK headers (including Authorization)
  * Null and empty custom headers handled gracefully
  * Immutability of custom headers map
  * Integration with datafile access token

Quality Assurance:
- Tests: 7/7 new tests passed, all existing tests pass
- Code Review: Manual review completed - follows Java SDK conventions
- Implementation: Builder pattern, immutability, proper header override logic

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: raju-opti

core-httpclient-impl/src/main/java/com/optimizely/ab/config/HttpProjectConfigManager.java

@@ -35,6 +35,8 @@
 
 import java.io.IOException;
 import java.net.URI;
+import java.util.Map;
+import java.util.HashMap;
 import java.util.concurrent.TimeUnit;
 
 /**
@@ -66,6 +68,7 @@ public class HttpProjectConfigManager extends PollingProjectConfigManager {
     public final OptimizelyHttpClient httpClient;
     private final URI uri;
     private final String datafileAccessToken;
+    private final Map<String, String> customHeaders;
     private String datafileLastModified;
     private final ReentrantLock lock = new ReentrantLock();
 
@@ -74,6 +77,7 @@ private HttpProjectConfigManager(long period,
                                      OptimizelyHttpClient httpClient,
                                      String url,
                                      String datafileAccessToken,
+                                     Map<String, String> customHeaders,
                                      long blockingTimeoutPeriod,
                                      TimeUnit blockingTimeoutUnit,
                                      NotificationCenter notificationCenter,
@@ -82,6 +86,7 @@ private HttpProjectConfigManager(long period,
         this.httpClient = httpClient;
         this.uri = URI.create(url);
         this.datafileAccessToken = datafileAccessToken;
+        this.customHeaders = customHeaders != null ? new HashMap<>(customHeaders) : new HashMap<>();
     }
 
     public URI getUri() {
@@ -171,6 +176,7 @@ public void close() {
     HttpGet createHttpRequest() {
         HttpGet httpGet = new HttpGet(uri);
 
+        // Apply SDK headers first
         if (datafileAccessToken != null) {
             httpGet.setHeader(HttpHeaders.AUTHORIZATION, "Bearer " + datafileAccessToken);
         }
@@ -179,6 +185,13 @@ HttpGet createHttpRequest() {
             httpGet.setHeader(HttpHeaders.IF_MODIFIED_SINCE, datafileLastModified);
         }
 
+        // Apply custom headers last to allow user override of SDK headers
+        if (customHeaders != null && !customHeaders.isEmpty()) {
+            for (Map.Entry<String, String> header : customHeaders.entrySet()) {
+                httpGet.setHeader(header.getKey(), header.getValue());
+            }
+        }
+
         return httpGet;
     }
 
@@ -190,6 +203,7 @@ public static class Builder {
         private String datafile;
         private String url;
         private String datafileAccessToken = null;
+        private Map<String, String> customHeaders = null;
         private String format = "https://cdn.optimizely.com/datafiles/%s.json";
         private String authFormat = "https://config.optimizely.com/datafiles/auth/%s.json";
         private OptimizelyHttpClient httpClient;
@@ -222,6 +236,18 @@ public Builder withDatafileAccessToken(String token) {
             return this;
         }
 
+        /**
+         * Set custom headers to be included in HTTP requests to fetch the datafile.
+         * If a custom header has the same name as an SDK-added header, the custom header value will override it.
+         *
+         * @param customHeaders A map of header names to header values
+         * @return A HttpProjectConfigManager builder
+         */
+        public Builder withCustomHeaders(Map<String, String> customHeaders) {
+            this.customHeaders = customHeaders;
+            return this;
+        }
+
         public Builder withUrl(String url) {
             this.url = url;
             return this;
@@ -380,6 +406,7 @@ public HttpProjectConfigManager build(boolean defer) {
                 httpClient,
                 url,
                 datafileAccessToken,
+                customHeaders,
                 blockingTimeoutPeriod,
                 blockingTimeoutUnit,
                 notificationCenter,

core-httpclient-impl/src/test/java/com/optimizely/ab/config/HttpProjectConfigManagerTest.java

@@ -37,6 +37,8 @@
 
 import java.io.IOException;
 import java.net.URI;
+import java.util.Map;
+import java.util.HashMap;
 import java.util.concurrent.TimeUnit;
 
 import static com.optimizely.ab.config.HttpProjectConfigManager.*;
@@ -396,4 +398,159 @@ public void testBasicFetchTwice() throws Exception {
         ProjectConfig latestConfig = projectConfigManager.getConfig();
         assertEquals(actual, latestConfig);
     }
+
+    @Test
+    public void testCustomHeadersAreIncludedInRequest() throws Exception {
+        Map<String, String> customHeaders = new HashMap<>();
+        customHeaders.put("X-Custom-Header", "custom-value");
+        customHeaders.put("X-Another-Header", "another-value");
+
+        HttpProjectConfigManager manager = builder()
+            .withOptimizelyHttpClient(mockHttpClient)
+            .withSdkKey("test-sdk-key")
+            .withCustomHeaders(customHeaders)
+            .build(true);
+
+        try {
+            HttpGet request = manager.createHttpRequest();
+
+            // Verify custom headers are present
+            assertNotNull(request.getFirstHeader("X-Custom-Header"));
+            assertEquals("custom-value", request.getFirstHeader("X-Custom-Header").getValue());
+            assertNotNull(request.getFirstHeader("X-Another-Header"));
+            assertEquals("another-value", request.getFirstHeader("X-Another-Header").getValue());
+        } finally {
+            manager.close();
+        }
+    }
+
+    @Test
+    public void testCustomHeadersOverrideSdkHeaders() throws Exception {
+        Map<String, String> customHeaders = new HashMap<>();
+        // Override the Authorization header
+        customHeaders.put(HttpHeaders.AUTHORIZATION, "Bearer custom-token");
+
+        HttpProjectConfigManager manager = builder()
+            .withOptimizelyHttpClient(mockHttpClient)
+            .withSdkKey("test-sdk-key")
+            .withDatafileAccessToken("sdk-token")
+            .withCustomHeaders(customHeaders)
+            .build(true);
+
+        try {
+            HttpGet request = manager.createHttpRequest();
+
+            // Verify custom header overrides SDK header
+            assertNotNull(request.getFirstHeader(HttpHeaders.AUTHORIZATION));
+            assertEquals("Bearer custom-token", request.getFirstHeader(HttpHeaders.AUTHORIZATION).getValue());
+        } finally {
+            manager.close();
+        }
+    }
+
+    @Test
+    public void testWithoutCustomHeaders() throws Exception {
+        HttpProjectConfigManager manager = builder()
+            .withOptimizelyHttpClient(mockHttpClient)
+            .withSdkKey("test-sdk-key")
+            .build(true);
+
+        try {
+            HttpGet request = manager.createHttpRequest();
+
+            // Verify no custom headers are present (only SDK headers)
+            assertNull(request.getFirstHeader("X-Custom-Header"));
+        } finally {
+            manager.close();
+        }
+    }
+
+    @Test
+    public void testWithNullCustomHeaders() throws Exception {
+        HttpProjectConfigManager manager = builder()
+            .withOptimizelyHttpClient(mockHttpClient)
+            .withSdkKey("test-sdk-key")
+            .withCustomHeaders(null)
+            .build(true);
+
+        try {
+            HttpGet request = manager.createHttpRequest();
+
+            // Should not throw exception and should work normally
+            assertNotNull(request);
+        } finally {
+            manager.close();
+        }
+    }
+
+    @Test
+    public void testWithEmptyCustomHeaders() throws Exception {
+        Map<String, String> customHeaders = new HashMap<>();
+
+        HttpProjectConfigManager manager = builder()
+            .withOptimizelyHttpClient(mockHttpClient)
+            .withSdkKey("test-sdk-key")
+            .withCustomHeaders(customHeaders)
+            .build(true);
+
+        try {
+            HttpGet request = manager.createHttpRequest();
+
+            // Should not throw exception and should work normally
+            assertNotNull(request);
+        } finally {
+            manager.close();
+        }
+    }
+
+    @Test
+    public void testCustomHeadersWithDatafileAccessToken() throws Exception {
+        Map<String, String> customHeaders = new HashMap<>();
+        customHeaders.put("X-Custom-Header", "custom-value");
+
+        HttpProjectConfigManager manager = builder()
+            .withOptimizelyHttpClient(mockHttpClient)
+            .withSdkKey("test-sdk-key")
+            .withDatafileAccessToken("test-token")
+            .withCustomHeaders(customHeaders)
+            .build(true);
+
+        try {
+            HttpGet request = manager.createHttpRequest();
+
+            // Verify both custom headers and SDK headers are present
+            assertNotNull(request.getFirstHeader("X-Custom-Header"));
+            assertEquals("custom-value", request.getFirstHeader("X-Custom-Header").getValue());
+            assertNotNull(request.getFirstHeader(HttpHeaders.AUTHORIZATION));
+            assertEquals("Bearer test-token", request.getFirstHeader(HttpHeaders.AUTHORIZATION).getValue());
+        } finally {
+            manager.close();
+        }
+    }
+
+    @Test
+    public void testCustomHeadersAreImmutable() throws Exception {
+        Map<String, String> customHeaders = new HashMap<>();
+        customHeaders.put("X-Custom-Header", "original-value");
+
+        HttpProjectConfigManager manager = builder()
+            .withOptimizelyHttpClient(mockHttpClient)
+            .withSdkKey("test-sdk-key")
+            .withCustomHeaders(customHeaders)
+            .build(true);
+
+        try {
+            // Modify the original map after building
+            customHeaders.put("X-Custom-Header", "modified-value");
+            customHeaders.put("X-New-Header", "new-value");
+
+            HttpGet request = manager.createHttpRequest();
+
+            // Verify headers are not affected by external map modifications
+            assertEquals("original-value", request.getFirstHeader("X-Custom-Header").getValue());
+            assertNull(request.getFirstHeader("X-New-Header"));
+        } finally {
+            manager.close();
+        }
+    }
 }