feat(flagd): Add features to customize auth to Sync API server (authorityOverride and clientInterceptors)

providers/flagd/README.md

@@ -110,6 +110,7 @@ Given below are the supported configurations:
 | port                  | FLAGD_PORT                     | int                      | 8013      | rpc & in-process        |
 | targetUri             | FLAGD_TARGET_URI               | string                   | null      | rpc & in-process        |
 | tls                   | FLAGD_TLS                      | boolean                  | false     | rpc & in-process        |
+| defaultAuthority      | FLAGD_DEFAULT_AUTHORITY        | String                   | null      | rpc & in-process        |
 | socketPath            | FLAGD_SOCKET_PATH              | String                   | null      | rpc & in-process        |
 | certPath              | FLAGD_SERVER_CERT_PATH         | String                   | null      | rpc & in-process        |
 | deadline              | FLAGD_DEADLINE_MS              | int                      | 500       | rpc & in-process & file |
@@ -180,6 +181,50 @@ FlagdProvider flagdProvider = new FlagdProvider(
 > There's a [vulnerability](https://security.snyk.io/vuln/SNYK-JAVA-IONETTY-1042268) in [netty](https://github.com/netty/netty), a transitive dependency of the underlying gRPC libraries used in the flagd-provider that fails to correctly validate certificates.
 > This will be addressed in netty v5.
 
+### Configuring gRPC credentials and headers
+
+The `clientInterceptors` and `defaultAuthority` are meant for connection of the in-process resolver to a Sync API implementation on a host/port, that might require special credentials or headers.
+
+```java
+private static ClientInterceptor createHeaderInterceptor() {
+    return new ClientInterceptor() {
+        @Override
+        public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next) {
+            return new ForwardingClientCall.SimpleForwardingClientCall<ReqT, RespT>(next.newCall(method, callOptions)) {
+                @Override
+                public void start(Listener<RespT> responseListener, Metadata headers) {
+                    headers.put(Metadata.Key.of("custom-header", Metadata.ASCII_STRING_MARSHALLER), "header-value");
+                    super.start(responseListener, headers);
+                }
+            };
+        }
+    };
+}
+
+private static ClientInterceptor createCallCrednetialsInterceptor(CallCredentials callCredentials) throws IOException {
+    return new ClientInterceptor() {
+        @Override
+        public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next) {
+            return next.newCall(method, callOptions.withCallCredentials(callCredentials));
+        }
+    };
+}
+
+List<ClientInterceptor> clientInterceptors = new ArrayList<ClientInterceptor>(2);
+clientInterceptors.add(createHeaderInterceptor());
+CallCredentials myCallCredentals = ...;
+clientInterceptors.add(createCallCrednetialsInterceptor(myCallCredentials));
+
+FlagdProvider flagdProvider = new FlagdProvider(
+        FlagdOptions.builder()
+                .host("example.com/flagdSyncApi")
+                .port(443)
+                .tls(true)
+                .defaultAuthority("authority-host.sync.example.com")
+                .clientInterceptors(clientInterceptors)
+                .build());
+```
+
 ### Caching (RPC only)
 
 > [!NOTE]  

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

@@ -24,6 +24,7 @@ public final class Config {
     static final String HOST_ENV_VAR_NAME = "FLAGD_HOST";
     static final String PORT_ENV_VAR_NAME = "FLAGD_PORT";
     static final String TLS_ENV_VAR_NAME = "FLAGD_TLS";
+    static final String DEFAULT_AUTHORITY_ENV_VAR_NAME = "FLAGD_DEFAULT_AUTHORITY";
     static final String SOCKET_PATH_ENV_VAR_NAME = "FLAGD_SOCKET_PATH";
     static final String SERVER_CERT_PATH_ENV_VAR_NAME = "FLAGD_SERVER_CERT_PATH";
     static final String CACHE_ENV_VAR_NAME = "FLAGD_CACHE";

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

@@ -7,8 +7,10 @@
 import dev.openfeature.sdk.EvaluationContext;
 import dev.openfeature.sdk.ImmutableContext;
 import dev.openfeature.sdk.Structure;
+import io.grpc.ClientInterceptor;
 import io.opentelemetry.api.GlobalOpenTelemetry;
 import io.opentelemetry.api.OpenTelemetry;
+import java.util.List;
 import java.util.function.Function;
 import lombok.Builder;
 import lombok.Getter;
@@ -164,6 +166,18 @@ public class FlagdOptions {
      */
     private OpenTelemetry openTelemetry;
 
+    /**
+     * gRPC client interceptors to be used when creating a gRPC channel.
+     */
+    @Builder.Default
+    private List<ClientInterceptor> clientInterceptors = null;
+
+    /**
+     * Authority header to be used when creating a gRPC channel.
+     */
+    @Builder.Default
+    private String defaultAuthority = fallBackToEnvOrDefault(Config.DEFAULT_AUTHORITY_ENV_VAR_NAME, null);
+
     /**
      * Builder overwrite in order to customize the "build" method.
      *

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

@@ -63,6 +63,12 @@ public static ManagedChannel nettyChannel(final FlagdOptions options) {
             final NettyChannelBuilder builder =
                     NettyChannelBuilder.forTarget(targetUri).keepAliveTime(keepAliveMs, TimeUnit.MILLISECONDS);
 
+            if (options.getDefaultAuthority() != null) {
+                builder.overrideAuthority(options.getDefaultAuthority());
+            }
+            if (options.getClientInterceptors() != null) {
+                builder.intercept(options.getClientInterceptors());
+            }
             if (options.isTls()) {
                 SslContextBuilder sslContext = GrpcSslContexts.forClient();
 

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

@@ -20,7 +20,10 @@
 
 import dev.openfeature.contrib.providers.flagd.resolver.process.storage.MockConnector;
 import dev.openfeature.contrib.providers.flagd.resolver.process.storage.connector.Connector;
+import io.grpc.ClientInterceptor;
 import io.opentelemetry.api.OpenTelemetry;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.function.Function;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
@@ -46,12 +49,15 @@ void TestDefaults() {
         assertNull(builder.getOfflineFlagSourcePath());
         assertEquals(Resolver.RPC, builder.getResolverType());
         assertEquals(0, builder.getKeepAlive());
+        assertNull(builder.getDefaultAuthority());
+        assertNull(builder.getClientInterceptors());
     }
 
     @Test
     void TestBuilderOptions() {
         OpenTelemetry openTelemetry = Mockito.mock(OpenTelemetry.class);
         Connector connector = new MockConnector(null);
+        List<ClientInterceptor> clientInterceptors = new ArrayList<ClientInterceptor>();
 
         FlagdOptions flagdOptions = FlagdOptions.builder()
                 .host("https://hosted-flagd")
@@ -66,6 +72,8 @@ void TestBuilderOptions() {
                 .resolverType(Resolver.IN_PROCESS)
                 .targetUri("dns:///localhost:8016")
                 .keepAlive(1000)
+                .defaultAuthority("test-authority.sync.example.com")
+                .clientInterceptors(clientInterceptors)
                 .build();
 
         assertEquals("https://hosted-flagd", flagdOptions.getHost());
@@ -80,6 +88,8 @@ void TestBuilderOptions() {
         assertEquals(Resolver.IN_PROCESS, flagdOptions.getResolverType());
         assertEquals("dns:///localhost:8016", flagdOptions.getTargetUri());
         assertEquals(1000, flagdOptions.getKeepAlive());
+        assertEquals("test-authority.sync.example.com", flagdOptions.getDefaultAuthority());
+        assertEquals(clientInterceptors, flagdOptions.getClientInterceptors());
     }
 
     @Test

providers/flagd/src/test/java/dev/openfeature/contrib/providers/flagd/resolver/common/ChannelBuilderTest.java

@@ -2,6 +2,7 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.mockito.ArgumentMatchers.anyList;
 import static org.mockito.Mockito.any;
 import static org.mockito.Mockito.anyLong;
 import static org.mockito.Mockito.anyString;
@@ -11,6 +12,7 @@
 import static org.mockito.Mockito.when;
 
 import dev.openfeature.contrib.providers.flagd.FlagdOptions;
+import io.grpc.ClientInterceptor;
 import io.grpc.ManagedChannel;
 import io.grpc.netty.GrpcSslContexts;
 import io.grpc.netty.NettyChannelBuilder;
@@ -20,6 +22,8 @@
 import io.netty.channel.unix.DomainSocketAddress;
 import io.netty.handler.ssl.SslContextBuilder;
 import java.io.File;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.concurrent.TimeUnit;
 import javax.net.ssl.SSLKeyException;
 import org.junit.jupiter.api.Test;
@@ -113,6 +117,83 @@ void testNettyChannel_withTlsAndCert() {
         }
     }
 
+    @Test
+    void testNettyChannel_withDefaultAuthority() {
+        try (MockedStatic<NettyChannelBuilder> nettyMock = mockStatic(NettyChannelBuilder.class)) {
+            // Mocks
+            NettyChannelBuilder mockBuilder = mock(NettyChannelBuilder.class);
+            ManagedChannel mockChannel = mock(ManagedChannel.class);
+            nettyMock
+                    .when(() -> NettyChannelBuilder.forTarget("localhost:8080"))
+                    .thenReturn(mockBuilder);
+
+            when(mockBuilder.keepAliveTime(anyLong(), any(TimeUnit.class))).thenReturn(mockBuilder);
+            when(mockBuilder.sslContext(any())).thenReturn(mockBuilder);
+            when(mockBuilder.overrideAuthority(anyString())).thenReturn(mockBuilder);
+            when(mockBuilder.build()).thenReturn(mockChannel);
+
+            // Input options
+            FlagdOptions options = FlagdOptions.builder()
+                    .host("localhost")
+                    .port(8080)
+                    .keepAlive(5000)
+                    .tls(true)
+                    .defaultAuthority("test-authority.sync.example.com")
+                    .build();
+
+            // Call method under test
+            ManagedChannel channel = ChannelBuilder.nettyChannel(options);
+
+            // Assertions
+            assertThat(channel).isEqualTo(mockChannel);
+            nettyMock.verify(() -> NettyChannelBuilder.forTarget("localhost:8080"));
+            verify(mockBuilder).keepAliveTime(5000, TimeUnit.MILLISECONDS);
+            verify(mockBuilder).sslContext(any());
+            verify(mockBuilder).overrideAuthority("test-authority.sync.example.com");
+            verify(mockBuilder).build();
+        }
+    }
+
+    @Test
+    void testNettyChannel_withClientInterceptors() {
+        try (MockedStatic<NettyChannelBuilder> nettyMock = mockStatic(NettyChannelBuilder.class)) {
+            // Mocks
+            NettyChannelBuilder mockBuilder = mock(NettyChannelBuilder.class);
+            ManagedChannel mockChannel = mock(ManagedChannel.class);
+            nettyMock
+                    .when(() -> NettyChannelBuilder.forTarget("localhost:8080"))
+                    .thenReturn(mockBuilder);
+
+            when(mockBuilder.keepAliveTime(anyLong(), any(TimeUnit.class))).thenReturn(mockBuilder);
+            when(mockBuilder.sslContext(any())).thenReturn(mockBuilder);
+            when(mockBuilder.intercept(anyList())).thenReturn(mockBuilder);
+            when(mockBuilder.build()).thenReturn(mockChannel);
+
+            List<ClientInterceptor> clientInterceptors = new ArrayList<ClientInterceptor>();
+            clientInterceptors.add(mock(ClientInterceptor.class));
+
+            // Input options
+            FlagdOptions options = FlagdOptions.builder()
+                    .host("localhost")
+                    .port(8080)
+                    .keepAlive(5000)
+                    .tls(true)
+                    .clientInterceptors(clientInterceptors)
+                    .build();
+
+            // Call method under test
+            ManagedChannel channel = ChannelBuilder.nettyChannel(options);
+
+            // Assertions
+            assertThat(channel).isEqualTo(mockChannel);
+            nettyMock.verify(() -> NettyChannelBuilder.forTarget("localhost:8080"));
+            verify(mockBuilder).keepAliveTime(5000, TimeUnit.MILLISECONDS);
+            verify(mockBuilder).sslContext(any());
+            verify(mockBuilder).intercept(clientInterceptors);
+            verify(mockBuilder).build();
+        }
+    }
+
     @ParameterizedTest
     @ValueSource(strings = {"/incorrect/{uri}/;)"})
     void testNettyChannel_withInvalidTargetUri(String uri) {