feat: allow reusing an existing OkHttpClient via DefaultHttpClient.Bu… (#936)

Author: tanya732

.fernignore

@@ -70,6 +70,7 @@ src/test/java/com/auth0/client/mgmt/OAuthTokenSupplierTest.java
 src/test/java/com/auth0/client/mgmt/ManagementApiBuilderTest.java
 src/test/java/com/auth0/client/mgmt/CustomDomainInterceptorTest.java
 src/test/java/com/auth0/client/mgmt/CustomDomainHeaderIntegrationTest.java
+src/test/java/com/auth0/net/client/DefaultHttpClientTest.java
 
 # Configuration files from auth0-real
 .codecov.yml

EXAMPLES.md

@@ -65,6 +65,35 @@ If the `DefaultHttpClient` does not support your required networking client conf
 your own client by implementing the `Auth0HttpClient` interface and providing it to the API client. This is an advanced
 use case and should be used only when necessary.
 
+If you already have a configured `OkHttpClient` (for example, one shared across your application with a custom connection
+pool, dispatcher, timeouts, or interceptors), you can reuse it as the base for the `DefaultHttpClient` via `withClient`:
+
+```java
+OkHttpClient okHttpClient = new OkHttpClient.Builder()
+        // your shared transport configuration, e.g. timeouts, dispatcher, or a custom interceptor
+        .build();
+
+Auth0HttpClient httpClient = DefaultHttpClient.newBuilder()
+        .withClient(okHttpClient)
+        .build();
+
+AuthAPI auth = AuthAPI.newBuilder("{YOUR_DOMAIN}", "{YOUR_CLIENT_ID}", "{YOUR_CLIENT_SECRET}")
+        .withHttpClient(httpClient)
+        .build();
+```
+
+When you supply a client this way, **you own its transport configuration**: timeouts, dispatcher, connection pool, cache,
+proxy, and any interceptors on it are used as-is. The corresponding `DefaultHttpClient.Builder` transport settings
+(`withReadTimeout`, `withConnectTimeout`, `withMaxRequests`, `withMaxRequestsPerHost`, `withProxy`) are ignored in this
+case, so your client is never silently overridden — configure those on your own `OkHttpClient` instead.
+
+The SDK's own behavior is always layered on top and cannot be bypassed: the Auth0 telemetry, rate-limit handling, and
+logging interceptors are added to your client. These remain configurable via `withTelemetry`, `telemetryEnabled`,
+`withMaxRetries`, and `withLogging`.
+
+> If you do not supply a client, nothing changes: the `DefaultHttpClient.Builder` builds and fully configures the
+> transport as before.
+
 ### Management API
 
 The Management API client uses `ManagementApi` as the main entry point.

src/main/java/com/auth0/net/client/DefaultHttpClient.java

@@ -25,9 +25,10 @@
  * API clients.
  * </p>
  * <p>
- * For most use cases, usage of this client is recommended. If you have more advanced use cases,
- * such as the need to re-use an existing HTTP client, you may consider providing a custom
- * implementation of {@link Auth0HttpClient}.
+ * For most use cases, usage of this client is recommended. To reuse an existing {@link OkHttpClient}
+ * and its transport configuration, use {@link Builder#withClient(OkHttpClient)}. Only for advanced use
+ * cases not covered by the {@link Builder} should you provide a custom implementation of
+ * {@link Auth0HttpClient}.
  * </p>
  */
 public class DefaultHttpClient implements Auth0HttpClient {
@@ -55,15 +56,30 @@ OkHttpClient getOkClient() {
     }
 
     private DefaultHttpClient(Builder builder) {
-        okhttp3.OkHttpClient.Builder clientBuilder = new okhttp3.OkHttpClient.Builder();
-        clientBuilder.readTimeout(sanitizeTimeout(builder.readTimeout), TimeUnit.SECONDS);
-        clientBuilder.connectTimeout(sanitizeTimeout(builder.connectTimeout), TimeUnit.SECONDS);
+        okhttp3.OkHttpClient.Builder clientBuilder;
+        if (builder.baseClient != null) {
+            // A caller-supplied client owns all transport configuration: timeouts, dispatcher, connection
+            // pool, cache, proxy, and any interceptors already registered on it are used as-is. The transport
+            // settings on this builder (timeouts, dispatcher, proxy) are intentionally NOT applied here, so
+            // they never silently override the caller's client. The SDK's behavior interceptors are still
+            // layered on below.
+            clientBuilder = builder.baseClient.newBuilder();
+        } else {
+            // Default path (unchanged): the SDK builds and fully configures the transport.
+            clientBuilder = new okhttp3.OkHttpClient.Builder();
+            clientBuilder.readTimeout(sanitizeTimeout(builder.readTimeout), TimeUnit.SECONDS);
+            clientBuilder.connectTimeout(sanitizeTimeout(builder.connectTimeout), TimeUnit.SECONDS);
+            clientBuilder.dispatcher(getDispatcher(builder.maxRequests, builder.maxRequestsPerHost));
+            configureProxy(clientBuilder, builder.proxyOptions);
+        }
+
+        // SDK behavior is always applied regardless of the transport client, so Auth0 telemetry, rate-limit
+        // handling, and logging are guaranteed. These interceptors are parameterized by this builder
+        // (withTelemetry/withLogging/withMaxRetries), which remain effective even when a base client is used.
         clientBuilder.addInterceptor(getLoggingInterceptor(builder.loggingOptions));
         clientBuilder.addInterceptor(getTelemetryInterceptor(builder.telemetryEnabled, builder.telemetry));
         clientBuilder.addInterceptor(getRateLimitInterceptor(builder.maxRetries));
-        clientBuilder.dispatcher(getDispatcher(builder.maxRequests, builder.maxRequestsPerHost));
 
-        configureProxy(clientBuilder, builder.proxyOptions);
         this.client = clientBuilder.build();
     }
 
@@ -288,13 +304,15 @@ public static class Builder {
         private int maxRetries = 3;
         private int maxRequests = 64;
         private int maxRequestsPerHost = 5;
+        private OkHttpClient baseClient;
 
         /**
          * Sets the value of the read timeout, in seconds. Defaults to ten seconds. A value of zero results in no read timeout.
          * Negative numbers will be treated as zero.
          *
          * @param readTimeout the value of the read timeout to use.
          * @return this builder instance.
+         * @see #withClient(OkHttpClient) ignored when a base client is supplied.
          */
         public Builder withReadTimeout(int readTimeout) {
             this.readTimeout = readTimeout;
@@ -306,6 +324,7 @@ public Builder withReadTimeout(int readTimeout) {
          * Negative numbers will be treated as zero.
          * @param connectTimeout the value of the connect timeout to use.
          * @return this builder instance.
+         * @see #withClient(OkHttpClient) ignored when a base client is supplied.
          */
         public Builder withConnectTimeout(int connectTimeout) {
             this.connectTimeout = connectTimeout;
@@ -327,6 +346,7 @@ public Builder withLogging(LoggingOptions loggingOptions) {
          *
          * @param proxyOptions the Proxy configuration options
          * @return this builder instance.
+         * @see #withClient(OkHttpClient) ignored when a base client is supplied.
          */
         public Builder withProxy(ProxyOptions proxyOptions) {
             this.proxyOptions = proxyOptions;
@@ -381,6 +401,7 @@ public Builder withMaxRetries(int maxRetries) {
          *
          * @param maxRequests the number of requests to execute concurrently. Must be equal to or greater than one.
          * @return this builder instance.
+         * @see #withClient(OkHttpClient) ignored when a base client is supplied.
          */
         public Builder withMaxRequests(int maxRequests) {
             this.maxRequests = maxRequests;
@@ -392,12 +413,42 @@ public Builder withMaxRequests(int maxRequests) {
          *
          * @param maxRequestsPerHost the maximum number of requests for each host to execute concurrently. Must be equal to or greater than one.
          * @return this builder instance.
+         * @see #withClient(OkHttpClient) ignored when a base client is supplied.
          */
         public Builder withMaxRequestsPerHost(int maxRequestsPerHost) {
             this.maxRequestsPerHost = maxRequestsPerHost;
             return this;
         }
 
+        /**
+         * Use an existing {@link OkHttpClient} as the base for this client, reusing all of its
+         * <strong>transport</strong> configuration as-is: timeouts, dispatcher, connection pool, cache,
+         * proxy, and any interceptors already registered on it.
+         * <p>
+         * When a base client is provided, the transport-related settings on this builder
+         * ({@link #withReadTimeout(int)}, {@link #withConnectTimeout(int)}, {@link #withMaxRequests(int)},
+         * {@link #withMaxRequestsPerHost(int)}, and {@link #withProxy(ProxyOptions)}) are
+         * <strong>ignored</strong>. This is deliberate: your client's configuration is never silently
+         * overridden. Configuring those concerns is your responsibility, on the {@code OkHttpClient} you
+         * supply.
+         * </p>
+         * <p>
+         * The SDK's own behavior is always layered on top and cannot be bypassed: the Auth0 telemetry,
+         * rate-limit handling, and logging interceptors are added to your client. These remain configurable
+         * via {@link #withTelemetry(String, String)}, {@link #telemetryEnabled(boolean)},
+         * {@link #withMaxRetries(int)}, and {@link #withLogging(LoggingOptions)}, which stay effective even
+         * when a base client is used.
+         * </p>
+         *
+         * @param baseClient the {@link OkHttpClient} whose transport configuration should be reused.
+         * @return this builder instance.
+         */
+        public Builder withClient(OkHttpClient baseClient) {
+            Asserts.assertNotNull(baseClient, "base client");
+            this.baseClient = baseClient;
+            return this;
+        }
+
         /**
          * Create a {@code DefaultHttpClient} from this configured builder.
          * @return the created {@code DefaultHttpClient}.

src/test/java/com/auth0/client/auth/AuthAPITest.java

@@ -37,6 +37,7 @@
 import java.util.*;
 import java.util.concurrent.CompletableFuture;
 import java.util.stream.Collectors;
+import okhttp3.OkHttpClient;
 import okhttp3.mockwebserver.RecordedRequest;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
@@ -299,6 +300,31 @@ public void shouldSendCustomTelemetryWhenConfigured() throws Exception {
         assertThat(telemetry.get("version").asText(), is("1.2.3"));
     }
 
+    @Test
+    public void shouldReuseBaseClientAndPreserveSdkBehavior() throws Exception {
+        OkHttpClient baseClient = new OkHttpClient.Builder()
+                .addInterceptor(chain -> chain.proceed(chain.request()
+                        .newBuilder()
+                        .addHeader("X-Custom-Base", "base-client")
+                        .build()))
+                .build();
+
+        AuthAPI customApi = AuthAPI.newBuilder(server.getBaseUrl(), CLIENT_ID, CLIENT_SECRET)
+                .withHttpClient(
+                        DefaultHttpClient.newBuilder().withClient(baseClient).build())
+                .build();
+
+        Request<UserInfo> request = customApi.userInfo("accessToken");
+        server.jsonResponse(AUTH_USER_INFO, 200);
+        request.execute();
+
+        RecordedRequest recordedRequest = server.takeRequest();
+        // The base client's interceptor is carried over via newBuilder(), so the user's config is preserved.
+        assertThat(recordedRequest.getHeader("X-Custom-Base"), is("base-client"));
+        // SDK behavior (telemetry) is still layered on top, so integrity is preserved.
+        assertThat(recordedRequest.getHeader("Auth0-Client"), is(notNullValue()));
+    }
+
     @Test
     public void shouldNestAuth0JavaInTelemetryEnv() throws Exception {
         String value = new Telemetry("my-wrapper-sdk", "1.2.3", "auth0-java-9.9.9").getValue();

src/test/java/com/auth0/net/client/DefaultHttpClientTest.java

@@ -0,0 +1,69 @@
+package com.auth0.net.client;
+
+import static com.auth0.AssertsUtil.verifyThrows;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.not;
+
+import java.util.concurrent.TimeUnit;
+import okhttp3.OkHttpClient;
+import org.junit.jupiter.api.Test;
+
+public class DefaultHttpClientTest {
+
+    @Test
+    public void shouldReuseBaseClientTransportConfigAndIgnoreBuilderTransportSettings() {
+        OkHttpClient baseClient =
+                new OkHttpClient.Builder().readTimeout(42, TimeUnit.SECONDS).build();
+        baseClient.dispatcher().setMaxRequests(7);
+
+        DefaultHttpClient httpClient = DefaultHttpClient.newBuilder()
+                .withClient(baseClient)
+                // Transport settings below must be ignored when a base client is supplied.
+                .withReadTimeout(99)
+                .withMaxRequests(99)
+                .build();
+
+        OkHttpClient built = httpClient.getOkClient();
+        assertThat(built.readTimeoutMillis(), is(42_000));
+        assertThat(built.dispatcher().getMaxRequests(), is(7));
+    }
+
+    @Test
+    public void shouldApplyBuilderTransportSettingsWhenNoBaseClient() {
+        DefaultHttpClient httpClient = DefaultHttpClient.newBuilder()
+                .withReadTimeout(42)
+                .withMaxRequests(7)
+                .build();
+
+        OkHttpClient built = httpClient.getOkClient();
+        assertThat(built.readTimeoutMillis(), is(42_000));
+        assertThat(built.dispatcher().getMaxRequests(), is(7));
+    }
+
+    @Test
+    public void shouldLayerSdkInterceptorsOnTopOfBaseClientInterceptors() {
+        OkHttpClient baseClient = new OkHttpClient.Builder()
+                .addInterceptor(chain -> chain.proceed(chain.request()))
+                .build();
+        int baseInterceptorCount = baseClient.interceptors().size();
+
+        DefaultHttpClient httpClient =
+                DefaultHttpClient.newBuilder().withClient(baseClient).build();
+
+        // The base client's interceptor plus the three SDK interceptors (logging, telemetry, rate-limit).
+        assertThat(httpClient.getOkClient().interceptors().size(), is(baseInterceptorCount + 3));
+        // The original base client is left untouched.
+        assertThat(
+                baseClient.interceptors().size(),
+                is(not(httpClient.getOkClient().interceptors().size())));
+    }
+
+    @Test
+    public void shouldThrowWhenBaseClientIsNull() {
+        verifyThrows(
+                IllegalArgumentException.class,
+                () -> DefaultHttpClient.newBuilder().withClient(null),
+                "'base client' cannot be null!");
+    }
+}