Add regression test for client mTLS without custom CA

Author: Debashismitra01

exporters/otlp/testing-internal/src/main/java/io/opentelemetry/exporter/otlp/testing/internal/AbstractHttpTelemetryExporterTest.java

@@ -30,6 +30,7 @@
 import com.linecorp.armeria.testing.junit5.server.SelfSignedCertificateExtension;
 import com.linecorp.armeria.testing.junit5.server.ServerExtension;
 import io.github.netmikey.logunit.api.LogCapturer;
+import io.netty.handler.ssl.ClientAuth;
 import io.opentelemetry.common.ComponentLoader;
 import io.opentelemetry.exporter.internal.FailedExportException;
 import io.opentelemetry.exporter.internal.TlsUtil;
@@ -159,6 +160,41 @@ protected void configure(ServerBuilder sb) {
         }
       };
 
+  // Separate server that requires client authentication.
+  // Used to verify client mTLS works even when no custom trust
+  // certificates are configured.
+  @RegisterExtension
+  @Order(4)
+  static final ServerExtension mtlsServer = new ServerExtension() {
+    @Override
+    protected void configure(ServerBuilder sb) {
+      sb.service(
+          "/v1/traces",
+          new CollectorService<>(
+              ExportTraceServiceRequest::parseFrom,
+              ExportTraceServiceRequest::getResourceSpansList));
+      sb.service(
+          "/v1/metrics",
+          new CollectorService<>(
+              ExportMetricsServiceRequest::parseFrom,
+              ExportMetricsServiceRequest::getResourceMetricsList));
+      sb.service(
+          "/v1/logs",
+          new CollectorService<>(
+              ExportLogsServiceRequest::parseFrom,
+              ExportLogsServiceRequest::getResourceLogsList));
+
+      sb.http(0);
+      sb.https(0);
+      sb.tls(TlsKeyPair.of(certificate.privateKey(), certificate.certificate()));
+      sb.tlsCustomizer(
+          ssl -> {
+            ssl.trustManager(clientCertificate.certificate());
+            ssl.clientAuth(ClientAuth.REQUIRE);
+          });
+    }
+  };
+
   private static class CollectorService<T> implements HttpService {
     private final ThrowingExtractor<byte[], T, InvalidProtocolBufferException> parse;
     private final Function<T, List<? extends Object>> getResourceTelemetry;
@@ -461,6 +497,24 @@ void clientTls(byte[] privateKey) throws Exception {
     }
   }
 
+  @ParameterizedTest
+  @ArgumentsSource(ClientPrivateKeyProvider.class)
+  void clientTlsWithoutTrustedCertificates(byte[] privateKey) throws Exception {
+    try (TelemetryExporter<T> exporter =
+        exporterBuilder()
+            .setEndpoint(mtlsServer.httpsUri() + path)
+            // Intentionally DO NOT configure trusted certificates.
+            .setClientTls(
+                privateKey,
+                Files.readAllBytes(clientCertificate.certificateFile().toPath()))
+            .build()) {
+
+      CompletableResultCode result =
+          exporter.export(Collections.singletonList(generateFakeTelemetry()));
+
+      assertThat(result.join(10, TimeUnit.SECONDS).isSuccess()).isTrue();
+    }
+  }
   private static class ClientPrivateKeyProvider implements ArgumentsProvider {
     @Override
     @SuppressWarnings("PrimitiveArrayPassedToVarargsMethod")