Added TracingProperties bean

without this change we removing all fields from an incoming request when propagating it further

with this change we're filtering out all remote fields cause they must be propagated

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/config/GatewayMetricsAutoConfiguration.java

@@ -27,6 +27,7 @@ import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.actuate.autoconfigure.metrics.CompositeMeterRegistryAutoConfiguration;
 import org.springframework.boot.actuate.autoconfigure.metrics.MetricsAutoConfiguration;
 import org.springframework.boot.actuate.autoconfigure.observation.ObservationAutoConfiguration;
+import org.springframework.boot.actuate.autoconfigure.tracing.TracingProperties;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 import org.springframework.boot.autoconfigure.AutoConfigureBefore;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
@@ -134,11 +135,12 @@ public class GatewayMetricsAutoConfiguration {
 
 			@Bean
 			@ConditionalOnMissingBean
-			@ConditionalOnBean(Propagator.class)
+			@ConditionalOnBean({ Propagator.class, TracingProperties.class })
 			@Order(Ordered.HIGHEST_PRECEDENCE + 5)
 			GatewayPropagatingSenderTracingObservationHandler gatewayPropagatingSenderTracingObservationHandler(
-					Tracer tracer, Propagator propagator) {
-				return new GatewayPropagatingSenderTracingObservationHandler(tracer, propagator);
+					Tracer tracer, Propagator propagator, TracingProperties tracingProperties) {
+				return new GatewayPropagatingSenderTracingObservationHandler(tracer, propagator,
+						tracingProperties.getBaggage().getRemoteFields());
 			}
 
 		}

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/filter/headers/observation/GatewayPropagatingSenderTracingObservationHandler.java

@@ -16,6 +16,8 @@
 
 package org.springframework.cloud.gateway.filter.headers.observation;
 
+import java.util.List;
+import java.util.Locale;
 import java.util.Objects;
 
 import io.micrometer.observation.Observation;
@@ -34,19 +36,26 @@ public class GatewayPropagatingSenderTracingObservationHandler
 
 	private final Propagator propagator;
 
+	private final List<String> remoteFieldsLowerCase;
+
 	/**
 	 * Creates a new instance of {@link PropagatingSenderTracingObservationHandler}.
 	 * @param tracer the tracer to use to record events
 	 * @param propagator the mechanism to propagate tracing information into the carrier
+	 * @param remoteFields remote fields to be propagated over the wire
 	 */
-	public GatewayPropagatingSenderTracingObservationHandler(Tracer tracer, Propagator propagator) {
+	public GatewayPropagatingSenderTracingObservationHandler(Tracer tracer, Propagator propagator,
+			List<String> remoteFields) {
 		super(tracer, propagator);
 		this.propagator = propagator;
+		this.remoteFieldsLowerCase = remoteFields.stream().map(s -> s.toLowerCase(Locale.ROOT)).toList();
 	}
 
 	@Override
 	public void onStart(GatewayContext context) {
-		this.propagator.fields().forEach(s -> Objects.requireNonNull(context.getCarrier()).remove(s));
+		this.propagator.fields().stream()
+				.filter(field -> !remoteFieldsLowerCase.contains(field.toLowerCase(Locale.ROOT)))
+				.forEach(s -> Objects.requireNonNull(context.getCarrier()).remove(s));
 		super.onStart(context);
 	}
 

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/config/GatewayMetricsAutoConfigurationTests.java

@@ -29,6 +29,7 @@ import org.mockito.Mockito;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.SpringBootConfiguration;
+import org.springframework.boot.actuate.autoconfigure.tracing.TracingProperties;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.test.autoconfigure.actuate.observability.AutoConfigureObservability;
 import org.springframework.boot.test.context.SpringBootTest;
@@ -178,6 +179,11 @@ public class GatewayMetricsAutoConfigurationTests {
 			return Mockito.mock(Propagator.class);
 		}
 
+		@Bean
+		TracingProperties tracingProperties() {
+			return new TracingProperties();
+		}
+
 	}
 
 	@SpringBootConfiguration

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/filter/headers/observation/B3BraveObservedHttpHeadersFilterTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.cloud.gateway.filter.headers.observation;
 
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
@@ -67,9 +68,11 @@ class B3BraveObservedHttpHeadersFilterTests {
 	void shouldWorkWithB3SingleHeader() {
 		TestObservationRegistry observationRegistry = TestObservationRegistry.create();
 		observationRegistry.observationConfig()
-				.observationHandler(new ObservationHandler.FirstMatchingCompositeObservationHandler(
-						new GatewayPropagatingSenderTracingObservationHandler(tracer, propagator),
-						new DefaultTracingObservationHandler(tracer)));
+				.observationHandler(
+						new ObservationHandler.FirstMatchingCompositeObservationHandler(
+								new GatewayPropagatingSenderTracingObservationHandler(tracer, propagator,
+										Collections.singletonList("X-A")),
+								new DefaultTracingObservationHandler(tracer)));
 
 		Observation.createNotStarted("parent", observationRegistry).observe(() -> {
 			// given

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/filter/headers/observation/GatewayPropagatingSenderTracingObservationHandlerTests.java

@@ -55,7 +55,7 @@ class GatewayPropagatingSenderTracingObservationHandlerTests {
 	};
 
 	GatewayPropagatingSenderTracingObservationHandler handler = new GatewayPropagatingSenderTracingObservationHandler(
-			tracer, propagator);
+			tracer, propagator, Collections.singletonList("remote"));
 
 	@Test
 	void shouldRemovePropagationFieldsFromTheRequestBeforePropagating() {
@@ -63,13 +63,15 @@ class GatewayPropagatingSenderTracingObservationHandlerTests {
 		headers.put("foo", Collections.singletonList("foo value"));
 		headers.put("bar", Collections.singletonList("bar value"));
 		headers.put("baz", Collections.singletonList("baz value"));
+		headers.put("remote", Collections.singletonList("remote value"));
 		MockServerHttpRequest request = MockServerHttpRequest.get("/get").build();
 		MockServerWebExchange serverWebExchange = MockServerWebExchange.from(request);
 		GatewayContext gatewayContext = new GatewayContext(headers, request, serverWebExchange);
 
 		handler.onStart(gatewayContext);
 
-		then(headers).doesNotContainKeys("foo", "bar").containsEntry("baz", Collections.singletonList("baz value"));
+		then(headers).doesNotContainKeys("foo", "bar").containsEntry("baz", Collections.singletonList("baz value"))
+				.containsEntry("remote", Collections.singletonList("remote value"));
 	}
 
 }

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/filter/headers/observation/ObservedHttpHeadersFilterTests.java

@@ -100,7 +100,8 @@ public class ObservedHttpHeadersFilterTests extends SampleTestRunner {
 	@Override
 	public BiConsumer<BuildingBlocks, Deque<ObservationHandler<? extends Observation.Context>>> customizeObservationHandlers() {
 		return (bb, observationHandlers) -> observationHandlers
-				.addFirst(new GatewayPropagatingSenderTracingObservationHandler(bb.getTracer(), bb.getPropagator()));
+				.addFirst(new GatewayPropagatingSenderTracingObservationHandler(bb.getTracer(), bb.getPropagator(),
+						Collections.emptyList()));
 	}
 
 }