Use endpoint auth hints with resolved scheme

client/client-api/src/main/java/software/amazon/smithy/java/client/core/ClientPipeline.java

@@ -189,10 +189,12 @@ private <I extends SerializableStruct, O extends SerializableStruct> O afterIden
         var identity = identityResult.unwrap();
         call.context.put(CallContext.IDENTITY, identity);
 
-        // TODO: what to do with supportedAuthSchemes of an endpoint?
         Endpoint endpoint = resolveEndpoint(call);
         call.context.put(CallContext.ENDPOINT, endpoint);
 
+        // Augment signer properties with endpoint auth scheme overrides if present.
+        resolvedAuthScheme = applyEndpointAuthSchemeOverrides(endpoint, resolvedAuthScheme);
+
         RequestT req = protocol.setServiceEndpoint(requestHook.request(), endpoint);
         var signResult = resolvedAuthScheme.sign(req);
         req = signResult.signedRequest();
@@ -311,6 +313,34 @@ private <I extends SerializableStruct, O extends SerializableStruct> Endpoint re
         return call.endpointResolver.resolveEndpoint(request);
     }
 
+    @SuppressWarnings("unchecked")
+    private <IdentityT extends Identity> ResolvedScheme<IdentityT, RequestT> applyEndpointAuthSchemeOverrides(
+            Endpoint endpoint,
+            ResolvedScheme<IdentityT, RequestT> resolvedScheme
+    ) {
+        var endpointAuthSchemes = endpoint.authSchemes();
+        if (!endpointAuthSchemes.isEmpty()) {
+            var schemeId = resolvedScheme.authScheme().schemeId().toString();
+            for (var endpointAuthScheme : endpointAuthSchemes) {
+                if (schemeId.equals(endpointAuthScheme.authSchemeId())) {
+                    var overrides = endpointAuthScheme.properties();
+                    if (overrides.isEmpty()) {
+                        return resolvedScheme;
+                    }
+                    // Apply the found overrides for the auth scheme.
+                    var merged = Context.create();
+                    resolvedScheme.signerProperties().copyTo(merged);
+                    for (var key : overrides) {
+                        merged.put((Context.Key<Object>) key, endpointAuthScheme.property(key));
+                    }
+                    return new ResolvedScheme<>(merged, resolvedScheme.authScheme(), resolvedScheme.identity());
+                }
+            }
+        }
+
+        return resolvedScheme;
+    }
+
     private <I extends SerializableStruct, O extends SerializableStruct> O deserialize(
             ClientCall<I, O> call,
             RequestT request,

client/client-core/src/test/java/software/amazon/smithy/java/client/core/ClientPipelineTest.java

@@ -13,17 +13,29 @@
 
 import java.time.Duration;
 import java.util.ArrayList;
+import java.util.List;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicReference;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
+import software.amazon.smithy.java.auth.api.SignResult;
+import software.amazon.smithy.java.auth.api.identity.Identity;
+import software.amazon.smithy.java.auth.api.identity.IdentityResolver;
+import software.amazon.smithy.java.auth.api.identity.IdentityResult;
 import software.amazon.smithy.java.aws.client.restjson.RestJsonClientProtocol;
+import software.amazon.smithy.java.client.core.auth.scheme.AuthScheme;
+import software.amazon.smithy.java.client.core.auth.scheme.AuthSchemeOption;
 import software.amazon.smithy.java.client.core.auth.scheme.AuthSchemeResolver;
+import software.amazon.smithy.java.client.core.endpoint.Endpoint;
+import software.amazon.smithy.java.client.core.endpoint.EndpointAuthScheme;
 import software.amazon.smithy.java.client.core.endpoint.EndpointResolver;
 import software.amazon.smithy.java.client.http.JavaHttpClientTransport;
 import software.amazon.smithy.java.client.http.mock.MockPlugin;
 import software.amazon.smithy.java.client.http.mock.MockQueue;
+import software.amazon.smithy.java.context.Context;
 import software.amazon.smithy.java.core.serde.document.Document;
 import software.amazon.smithy.java.dynamicclient.DynamicClient;
+import software.amazon.smithy.java.http.api.HttpRequest;
 import software.amazon.smithy.java.http.api.HttpResponse;
 import software.amazon.smithy.java.io.datastream.DataStream;
 import software.amazon.smithy.java.retries.api.AcquireInitialTokenRequest;
@@ -188,6 +200,65 @@ public Builder toBuilder() {
         assertThat(calls, contains("Acquire", "Refresh", "Success: 1"));
     }
 
+    @Test
+    public void endpointAuthSchemeOverridesAugmentSignerProperties() {
+        var service = ShapeId.from("smithy.example#Sprockets");
+        var testSchemeId = ShapeId.from("smithy.test#testAuth");
+        var TEST_KEY = Context.<String>key("test-signing-override");
+        var capturedProperties = new AtomicReference<Context>();
+
+        // Auth scheme with a signer that captures the properties it receives.
+        var testScheme = AuthScheme.of(
+                testSchemeId,
+                HttpRequest.class,
+                Identity.class,
+                (request, identity, properties) -> {
+                    capturedProperties.set(properties);
+                    return new SignResult<>(request);
+                });
+
+        // Endpoint resolver that returns an endpoint with an auth scheme override.
+        EndpointResolver endpointResolver = params -> Endpoint.builder()
+                .uri("https://example.com")
+                .addAuthScheme(
+                        EndpointAuthScheme.builder()
+                                .authSchemeId(testSchemeId.toString())
+                                .putProperty(TEST_KEY, "overridden-value")
+                                .build())
+                .build();
+
+        var mockQueue = new MockQueue()
+                .enqueue(HttpResponse.builder()
+                        .statusCode(200)
+                        .body(DataStream.ofString("{\"id\":\"1\"}"))
+                        .build());
+        var mock = MockPlugin.builder().addQueue(mockQueue).build();
+
+        var client = DynamicClient.builder()
+                .serviceId(service)
+                .model(MODEL)
+                .addPlugin(mock)
+                .endpointResolver(endpointResolver)
+                .authSchemeResolver(params -> List.of(new AuthSchemeOption(testSchemeId)))
+                .putSupportedAuthSchemes(testScheme)
+                .addIdentityResolver(new IdentityResolver<>() {
+                    @Override
+                    public IdentityResult<Identity> resolveIdentity(Context requestProperties) {
+                        return IdentityResult.of(new Identity() {});
+                    }
+
+                    @Override
+                    public Class<Identity> identityType() {
+                        return Identity.class;
+                    }
+                })
+                .build();
+
+        client.call("GetSprocket", Document.ofObject(Map.of("id", "1")));
+
+        assertThat(capturedProperties.get().get(TEST_KEY), equalTo("overridden-value"));
+    }
+
     private static final class Token implements RetryToken {
         int retry;