feat: support gRPC over proxy

providers/flagd/README.md

@@ -112,6 +112,7 @@ Given below are the supported configurations:
 | maxEventStreamRetries | FLAGD_MAX_EVENT_STREAM_RETRIES | int                      | 5         | rpc                 |
 | retryBackoffMs        | FLAGD_RETRY_BACKOFF_MS         | int                      | 1000      | rpc                 |
 | offlineFlagSourcePath | FLAGD_OFFLINE_FLAG_SOURCE_PATH | String                   | null      | in-process          |
+| authority             | FLAGD_AUTHORITY_OVERRIDE       | String                   | null      | rpc & in-process    |
 
 > [!NOTE]  
 > Some configurations are only applicable for RPC resolver.

providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/Config.java

@@ -35,6 +35,7 @@ public final class Config {
     static final String OFFLINE_SOURCE_PATH = "FLAGD_OFFLINE_FLAG_SOURCE_PATH";
     static final String KEEP_ALIVE_MS_ENV_VAR_NAME_OLD = "FLAGD_KEEP_ALIVE_TIME";
     static final String KEEP_ALIVE_MS_ENV_VAR_NAME = "FLAGD_KEEP_ALIVE_TIME_MS";
+    static final String AUTHORITY_OVERRIDE = "FLAGD_AUTHORITY_OVERRIDE";
 
     static final String RESOLVER_RPC = "rpc";
     static final String RESOLVER_IN_PROCESS = "in-process";

providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/FlagdOptions.java

@@ -96,7 +96,7 @@ public class FlagdOptions {
     /**
      * gRPC client KeepAlive in milliseconds. Disabled with 0.
      * Defaults to 0 (disabled).
-     * 
+     *
      **/
     @Builder.Default
     private long keepAlive = fallBackToEnvOrDefault(Config.KEEP_ALIVE_MS_ENV_VAR_NAME,
@@ -109,6 +109,16 @@ public class FlagdOptions {
     @Builder.Default
     private String offlineFlagSourcePath = fallBackToEnvOrDefault(Config.OFFLINE_SOURCE_PATH, null);
 
+
+    /**
+     * gRPC authority override.
+     * Setting this will allow user to override the system generated authority with
+     * user specified string. This is useful when running flagd gRPC sync service behind
+     * proxy e.g. envoy, istio etc.
+     */
+    @Builder.Default
+    private String authority = fallBackToEnvOrDefault(Config.AUTHORITY_OVERRIDE, null);
+
     /**
      * Inject a Custom Connector for fetching flags.
      */

providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/resolver/common/ChannelBuilder.java

@@ -53,6 +53,12 @@ public static ManagedChannel nettyChannel(final FlagdOptions options) {
             final NettyChannelBuilder builder = NettyChannelBuilder
                     .forAddress(options.getHost(), options.getPort())
                     .keepAliveTime(keepAliveMs, TimeUnit.MILLISECONDS);
+
+
+            if (options.getAuthority() != null) {
+                builder.overrideAuthority(options.getAuthority());
+            }
+
             if (options.isTls()) {
                 SslContextBuilder sslContext = GrpcSslContexts.forClient();
 

providers/flagd/src/test/java/dev/openfeature/contrib/providers/flagd/FlagdOptionsTest.java

@@ -34,6 +34,7 @@ void TestDefaults() {
         assertNull(builder.getOfflineFlagSourcePath());
         assertEquals(Resolver.RPC, builder.getResolverType());
         assertEquals(0, builder.getKeepAlive());
+        assertNull(builder.getAuthority());
     }
 
     @Test
@@ -55,6 +56,7 @@ void TestBuilderOptions() {
                 .customConnector(connector)
                 .resolverType(Resolver.IN_PROCESS)
                 .keepAlive(1000)
+                .authority("test.service")
                 .build();
 
         assertEquals("https://hosted-flagd", flagdOptions.getHost());
@@ -70,6 +72,7 @@ void TestBuilderOptions() {
         assertEquals(connector, flagdOptions.getCustomConnector());
         assertEquals(Resolver.IN_PROCESS, flagdOptions.getResolverType());
         assertEquals(1000, flagdOptions.getKeepAlive());
+        assertEquals("test.service", flagdOptions.getAuthority());
     }
 
 
@@ -187,4 +190,13 @@ void testRpcProviderFromEnv_portConfigured_usesConfiguredPort() {
         assertThat(flagdOptions.getPort()).isEqualTo(1534);
 
     }
+
+
+    @Test
+    @SetEnvironmentVariable(key = AUTHORITY_OVERRIDE, value = "test.service")
+    void testAuthorityOverrideFromEnv() {
+        FlagdOptions flagdOptions = FlagdOptions.builder().build();
+
+        assertThat(flagdOptions.getAuthority()).isEqualTo("test.service");
+    }
 }