Add Origin header validation

- Fixes #695
- Does not implement Host header validation yet

Signed-off-by: Daniel Garnier-Moiroux <git@garnier.wf>

mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/server/transport/WebFluxSseServerTransportProvider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025-2025 the original author or authors.
+ * Copyright 2025-2026 the original author or authors.
  */
 
 package io.modelcontextprotocol.server.transport;
@@ -7,6 +7,7 @@ package io.modelcontextprotocol.server.transport;
 import java.io.IOException;
 import java.time.Duration;
 import java.util.List;
+import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 
 import io.modelcontextprotocol.common.McpTransportContext;
@@ -132,6 +133,11 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 	 */
 	private KeepAliveScheduler keepAliveScheduler;
 
+	/**
+	 * Security validator for validating HTTP requests.
+	 */
+	private final ServerTransportSecurityValidator securityValidator;
+
 	/**
 	 * Constructs a new WebFlux SSE server transport provider instance.
 	 * @param jsonMapper The ObjectMapper to use for JSON serialization/deserialization of
@@ -144,22 +150,26 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 	 * @param keepAliveInterval The interval for sending keep-alive pings to clients.
 	 * @param contextExtractor The context extractor to use for extracting MCP transport
 	 * context from HTTP requests. Must not be null.
+	 * @param securityValidator The security validator for validating HTTP requests.
 	 * @throws IllegalArgumentException if either parameter is null
 	 */
 	private WebFluxSseServerTransportProvider(McpJsonMapper jsonMapper, String baseUrl, String messageEndpoint,
 			String sseEndpoint, Duration keepAliveInterval,
-			McpTransportContextExtractor<ServerRequest> contextExtractor) {
+			McpTransportContextExtractor<ServerRequest> contextExtractor,
+			ServerTransportSecurityValidator securityValidator) {
 		Assert.notNull(jsonMapper, "ObjectMapper must not be null");
 		Assert.notNull(baseUrl, "Message base path must not be null");
 		Assert.notNull(messageEndpoint, "Message endpoint must not be null");
 		Assert.notNull(sseEndpoint, "SSE endpoint must not be null");
 		Assert.notNull(contextExtractor, "Context extractor must not be null");
+		Assert.notNull(securityValidator, "Security validator must not be null");
 
 		this.jsonMapper = jsonMapper;
 		this.baseUrl = baseUrl;
 		this.messageEndpoint = messageEndpoint;
 		this.sseEndpoint = sseEndpoint;
 		this.contextExtractor = contextExtractor;
+		this.securityValidator = securityValidator;
 		this.routerFunction = RouterFunctions.route()
 			.GET(this.sseEndpoint, this::handleSseConnection)
 			.POST(this.messageEndpoint, this::handleMessage)
@@ -273,6 +283,14 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 			return ServerResponse.status(HttpStatus.SERVICE_UNAVAILABLE).bodyValue("Server is shutting down");
 		}
 
+		try {
+			Map<String, List<String>> headers = request.headers().asHttpHeaders();
+			this.securityValidator.validateHeaders(headers);
+		}
+		catch (ServerTransportSecurityException e) {
+			return ServerResponse.status(e.getStatusCode()).bodyValue(e.getMessage());
+		}
+
 		McpTransportContext transportContext = this.contextExtractor.extract(request);
 
 		return ServerResponse.ok()
@@ -332,6 +350,14 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 			return ServerResponse.status(HttpStatus.SERVICE_UNAVAILABLE).bodyValue("Server is shutting down");
 		}
 
+		try {
+			Map<String, List<String>> headers = request.headers().asHttpHeaders();
+			this.securityValidator.validateHeaders(headers);
+		}
+		catch (ServerTransportSecurityException e) {
+			return ServerResponse.status(e.getStatusCode()).bodyValue(e.getMessage());
+		}
+
 		if (request.queryParam("sessionId").isEmpty()) {
 			return ServerResponse.badRequest().bodyValue(new McpError("Session ID missing in message endpoint"));
 		}
@@ -436,6 +462,8 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 		private McpTransportContextExtractor<ServerRequest> contextExtractor = (
 				serverRequest) -> McpTransportContext.EMPTY;
 
+		private ServerTransportSecurityValidator securityValidator = ServerTransportSecurityValidator.NOOP;
+
 		/**
 		 * Sets the McpJsonMapper to use for JSON serialization/deserialization of MCP
 		 * messages.
@@ -513,6 +541,18 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 			return this;
 		}
 
+		/**
+		 * Sets the security validator for validating HTTP requests.
+		 * @param securityValidator The security validator to use. Must not be null.
+		 * @return this builder instance
+		 * @throws IllegalArgumentException if securityValidator is null
+		 */
+		public Builder securityValidator(ServerTransportSecurityValidator securityValidator) {
+			Assert.notNull(securityValidator, "Security validator must not be null");
+			this.securityValidator = securityValidator;
+			return this;
+		}
+
 		/**
 		 * Builds a new instance of {@link WebFluxSseServerTransportProvider} with the
 		 * configured settings.
@@ -522,7 +562,7 @@ public class WebFluxSseServerTransportProvider implements McpServerTransportProv
 		public WebFluxSseServerTransportProvider build() {
 			Assert.notNull(messageEndpoint, "Message endpoint must be set");
 			return new WebFluxSseServerTransportProvider(jsonMapper == null ? McpJsonMapper.getDefault() : jsonMapper,
-					baseUrl, messageEndpoint, sseEndpoint, keepAliveInterval, contextExtractor);
+					baseUrl, messageEndpoint, sseEndpoint, keepAliveInterval, contextExtractor, securityValidator);
 		}
 
 	}

mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/server/transport/WebFluxStatelessServerTransport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025-2025 the original author or authors.
+ * Copyright 2025-2026 the original author or authors.
  */
 
 package io.modelcontextprotocol.server.transport;
@@ -24,6 +24,7 @@ import reactor.core.publisher.Mono;
 
 import java.io.IOException;
 import java.util.List;
+import java.util.Map;
 
 /**
  * Implementation of a WebFlux based {@link McpStatelessServerTransport}.
@@ -46,15 +47,23 @@ public class WebFluxStatelessServerTransport implements McpStatelessServerTransp
 
 	private volatile boolean isClosing = false;
 
+	/**
+	 * Security validator for validating HTTP requests.
+	 */
+	private final ServerTransportSecurityValidator securityValidator;
+
 	private WebFluxStatelessServerTransport(McpJsonMapper jsonMapper, String mcpEndpoint,
-			McpTransportContextExtractor<ServerRequest> contextExtractor) {
+			McpTransportContextExtractor<ServerRequest> contextExtractor,
+			ServerTransportSecurityValidator securityValidator) {
 		Assert.notNull(jsonMapper, "jsonMapper must not be null");
 		Assert.notNull(mcpEndpoint, "mcpEndpoint must not be null");
 		Assert.notNull(contextExtractor, "contextExtractor must not be null");
+		Assert.notNull(securityValidator, "Security validator must not be null");
 
 		this.jsonMapper = jsonMapper;
 		this.mcpEndpoint = mcpEndpoint;
 		this.contextExtractor = contextExtractor;
+		this.securityValidator = securityValidator;
 		this.routerFunction = RouterFunctions.route()
 			.GET(this.mcpEndpoint, this::handleGet)
 			.POST(this.mcpEndpoint, this::handlePost)
@@ -96,6 +105,14 @@ public class WebFluxStatelessServerTransport implements McpStatelessServerTransp
 			return ServerResponse.status(HttpStatus.SERVICE_UNAVAILABLE).bodyValue("Server is shutting down");
 		}
 
+		try {
+			Map<String, List<String>> headers = request.headers().asHttpHeaders();
+			this.securityValidator.validateHeaders(headers);
+		}
+		catch (ServerTransportSecurityException e) {
+			return ServerResponse.status(e.getStatusCode()).bodyValue(e.getMessage());
+		}
+
 		McpTransportContext transportContext = this.contextExtractor.extract(request);
 
 		List<MediaType> acceptHeaders = request.headers().asHttpHeaders().getAccept();
@@ -160,6 +177,8 @@ public class WebFluxStatelessServerTransport implements McpStatelessServerTransp
 		private McpTransportContextExtractor<ServerRequest> contextExtractor = (
 				serverRequest) -> McpTransportContext.EMPTY;
 
+		private ServerTransportSecurityValidator securityValidator = ServerTransportSecurityValidator.NOOP;
+
 		private Builder() {
 			// used by a static method
 		}
@@ -205,6 +224,18 @@ public class WebFluxStatelessServerTransport implements McpStatelessServerTransp
 			return this;
 		}
 
+		/**
+		 * Sets the security validator for validating HTTP requests.
+		 * @param securityValidator The security validator to use. Must not be null.
+		 * @return this builder instance
+		 * @throws IllegalArgumentException if securityValidator is null
+		 */
+		public Builder securityValidator(ServerTransportSecurityValidator securityValidator) {
+			Assert.notNull(securityValidator, "Security validator must not be null");
+			this.securityValidator = securityValidator;
+			return this;
+		}
+
 		/**
 		 * Builds a new instance of {@link WebFluxStatelessServerTransport} with the
 		 * configured settings.
@@ -214,7 +245,7 @@ public class WebFluxStatelessServerTransport implements McpStatelessServerTransp
 		public WebFluxStatelessServerTransport build() {
 			Assert.notNull(mcpEndpoint, "Message endpoint must be set");
 			return new WebFluxStatelessServerTransport(jsonMapper == null ? McpJsonMapper.getDefault() : jsonMapper,
-					mcpEndpoint, contextExtractor);
+					mcpEndpoint, contextExtractor, securityValidator);
 		}
 
 	}

mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/server/transport/WebFluxStreamableServerTransportProvider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025-2025 the original author or authors.
+ * Copyright 2025-2026 the original author or authors.
  */
 
 package io.modelcontextprotocol.server.transport;
@@ -36,6 +36,7 @@ import reactor.core.publisher.Mono;
 import java.io.IOException;
 import java.time.Duration;
 import java.util.List;
+import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 
 /**
@@ -67,17 +68,24 @@ public class WebFluxStreamableServerTransportProvider implements McpStreamableSe
 
 	private KeepAliveScheduler keepAliveScheduler;
 
+	/**
+	 * Security validator for validating HTTP requests.
+	 */
+	private final ServerTransportSecurityValidator securityValidator;
+
 	private WebFluxStreamableServerTransportProvider(McpJsonMapper jsonMapper, String mcpEndpoint,
 			McpTransportContextExtractor<ServerRequest> contextExtractor, boolean disallowDelete,
-			Duration keepAliveInterval) {
+			Duration keepAliveInterval, ServerTransportSecurityValidator securityValidator) {
 		Assert.notNull(jsonMapper, "JsonMapper must not be null");
 		Assert.notNull(mcpEndpoint, "Message endpoint must not be null");
 		Assert.notNull(contextExtractor, "Context extractor must not be null");
+		Assert.notNull(securityValidator, "Security validator must not be null");
 
 		this.jsonMapper = jsonMapper;
 		this.mcpEndpoint = mcpEndpoint;
 		this.contextExtractor = contextExtractor;
 		this.disallowDelete = disallowDelete;
+		this.securityValidator = securityValidator;
 		this.routerFunction = RouterFunctions.route()
 			.GET(this.mcpEndpoint, this::handleGet)
 			.POST(this.mcpEndpoint, this::handlePost)
@@ -166,6 +174,14 @@ public class WebFluxStreamableServerTransportProvider implements McpStreamableSe
 			return ServerResponse.status(HttpStatus.SERVICE_UNAVAILABLE).bodyValue("Server is shutting down");
 		}
 
+		try {
+			Map<String, List<String>> headers = request.headers().asHttpHeaders();
+			this.securityValidator.validateHeaders(headers);
+		}
+		catch (ServerTransportSecurityException e) {
+			return ServerResponse.status(e.getStatusCode()).bodyValue(e.getMessage());
+		}
+
 		McpTransportContext transportContext = this.contextExtractor.extract(request);
 
 		return Mono.defer(() -> {
@@ -221,6 +237,14 @@ public class WebFluxStreamableServerTransportProvider implements McpStreamableSe
 			return ServerResponse.status(HttpStatus.SERVICE_UNAVAILABLE).bodyValue("Server is shutting down");
 		}
 
+		try {
+			Map<String, List<String>> headers = request.headers().asHttpHeaders();
+			this.securityValidator.validateHeaders(headers);
+		}
+		catch (ServerTransportSecurityException e) {
+			return ServerResponse.status(e.getStatusCode()).bodyValue(e.getMessage());
+		}
+
 		McpTransportContext transportContext = this.contextExtractor.extract(request);
 
 		List<MediaType> acceptHeaders = request.headers().asHttpHeaders().getAccept();
@@ -310,6 +334,14 @@ public class WebFluxStreamableServerTransportProvider implements McpStreamableSe
 			return ServerResponse.status(HttpStatus.SERVICE_UNAVAILABLE).bodyValue("Server is shutting down");
 		}
 
+		try {
+			Map<String, List<String>> headers = request.headers().asHttpHeaders();
+			this.securityValidator.validateHeaders(headers);
+		}
+		catch (ServerTransportSecurityException e) {
+			return ServerResponse.status(e.getStatusCode()).bodyValue(e.getMessage());
+		}
+
 		McpTransportContext transportContext = this.contextExtractor.extract(request);
 
 		return Mono.defer(() -> {
@@ -410,6 +442,8 @@ public class WebFluxStreamableServerTransportProvider implements McpStreamableSe
 
 		private Duration keepAliveInterval;
 
+		private ServerTransportSecurityValidator securityValidator = ServerTransportSecurityValidator.NOOP;
+
 		private Builder() {
 			// used by a static method
 		}
@@ -477,6 +511,18 @@ public class WebFluxStreamableServerTransportProvider implements McpStreamableSe
 			return this;
 		}
 
+		/**
+		 * Sets the security validator for validating HTTP requests.
+		 * @param securityValidator The security validator to use. Must not be null.
+		 * @return this builder instance
+		 * @throws IllegalArgumentException if securityValidator is null
+		 */
+		public Builder securityValidator(ServerTransportSecurityValidator securityValidator) {
+			Assert.notNull(securityValidator, "Security validator must not be null");
+			this.securityValidator = securityValidator;
+			return this;
+		}
+
 		/**
 		 * Builds a new instance of {@link WebFluxStreamableServerTransportProvider} with
 		 * the configured settings.
@@ -487,7 +533,7 @@ public class WebFluxStreamableServerTransportProvider implements McpStreamableSe
 			Assert.notNull(mcpEndpoint, "Message endpoint must be set");
 			return new WebFluxStreamableServerTransportProvider(
 					jsonMapper == null ? McpJsonMapper.getDefault() : jsonMapper, mcpEndpoint, contextExtractor,
-					disallowDelete, keepAliveInterval);
+					disallowDelete, keepAliveInterval, securityValidator);
 		}
 
 	}

mcp-spring/mcp-spring-webflux/src/test/java/io/modelcontextprotocol/security/WebFluxServerTransportSecurityIntegrationTests.java

@@ -0,0 +1,291 @@
+/*
+ * Copyright 2026-2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.security;
+
+import java.time.Duration;
+import java.util.stream.Stream;
+
+import io.modelcontextprotocol.client.McpClient;
+import io.modelcontextprotocol.client.McpSyncClient;
+import io.modelcontextprotocol.client.transport.WebClientStreamableHttpTransport;
+import io.modelcontextprotocol.client.transport.WebFluxSseClientTransport;
+import io.modelcontextprotocol.json.McpJsonMapper;
+import io.modelcontextprotocol.server.McpServer;
+import io.modelcontextprotocol.server.TestUtil;
+import io.modelcontextprotocol.server.transport.DefaultServerTransportSecurityValidator;
+import io.modelcontextprotocol.server.transport.WebFluxSseServerTransportProvider;
+import io.modelcontextprotocol.server.transport.WebFluxStatelessServerTransport;
+import io.modelcontextprotocol.server.transport.WebFluxStreamableServerTransportProvider;
+import io.modelcontextprotocol.spec.McpSchema;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.BeforeParameterizedClassInvocation;
+import org.junit.jupiter.params.Parameter;
+import org.junit.jupiter.params.ParameterizedClass;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+import reactor.core.publisher.Mono;
+import reactor.netty.DisposableServer;
+import reactor.netty.http.server.HttpServer;
+
+import org.springframework.http.server.reactive.HttpHandler;
+import org.springframework.http.server.reactive.ReactorHttpHandlerAdapter;
+import org.springframework.web.reactive.function.client.ClientRequest;
+import org.springframework.web.reactive.function.client.ClientResponse;
+import org.springframework.web.reactive.function.client.ExchangeFilterFunction;
+import org.springframework.web.reactive.function.client.ExchangeFunction;
+import org.springframework.web.reactive.function.client.WebClient;
+import org.springframework.web.reactive.function.server.RouterFunction;
+import org.springframework.web.reactive.function.server.RouterFunctions;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.junit.jupiter.api.Named.named;
+import static org.junit.jupiter.params.provider.Arguments.arguments;
+
+/**
+ * Test the header security validation for all transport types.
+ *
+ * @author Daniel Garnier-Moiroux
+ */
+@ParameterizedClass
+@MethodSource("transports")
+public class WebFluxServerTransportSecurityIntegrationTests {
+
+	private static final String DISALLOWED_ORIGIN = "https://malicious.example.com";
+
+	@Parameter
+	private static Transport transport;
+
+	private static DisposableServer httpServer;
+
+	private static String baseUrl;
+
+	@BeforeParameterizedClassInvocation
+	static void createTransportAndStartServer(Transport transport) {
+		var port = TestUtil.findAvailablePort();
+		baseUrl = "http://localhost:" + port;
+		startServer(transport.routerFunction(), port);
+	}
+
+	@AfterAll
+	static void afterAll() {
+		stopServer();
+	}
+
+	private McpSyncClient mcpClient;
+
+	private final TestOriginHeaderExchangeFilterFunction exchangeFilterFunction = new TestOriginHeaderExchangeFilterFunction();
+
+	@BeforeEach
+	void setUp() {
+		mcpClient = transport.createMcpClient(baseUrl, exchangeFilterFunction);
+	}
+
+	@AfterEach
+	void tearDown() {
+		mcpClient.close();
+	}
+
+	@Test
+	void originAllowed() {
+		exchangeFilterFunction.setOriginHeader(baseUrl);
+		var result = mcpClient.initialize();
+		var tools = mcpClient.listTools();
+
+		assertThat(result.protocolVersion()).isNotEmpty();
+		assertThat(tools.tools()).isEmpty();
+	}
+
+	@Test
+	void noOrigin() {
+		exchangeFilterFunction.setOriginHeader(null);
+		var result = mcpClient.initialize();
+		var tools = mcpClient.listTools();
+
+		assertThat(result.protocolVersion()).isNotEmpty();
+		assertThat(tools.tools()).isEmpty();
+	}
+
+	@Test
+	void connectOriginNotAllowed() {
+		exchangeFilterFunction.setOriginHeader(DISALLOWED_ORIGIN);
+		assertThatThrownBy(() -> mcpClient.initialize());
+	}
+
+	@Test
+	void messageOriginNotAllowed() {
+		exchangeFilterFunction.setOriginHeader(baseUrl);
+		mcpClient.initialize();
+		exchangeFilterFunction.setOriginHeader(DISALLOWED_ORIGIN);
+		assertThatThrownBy(() -> mcpClient.listTools());
+	}
+
+	// ----------------------------------------------------
+	// Server management
+	// ----------------------------------------------------
+
+	private static void startServer(RouterFunction<?> routerFunction, int port) {
+		HttpHandler httpHandler = RouterFunctions.toHttpHandler(routerFunction);
+		ReactorHttpHandlerAdapter adapter = new ReactorHttpHandlerAdapter(httpHandler);
+		httpServer = HttpServer.create().port(port).handle(adapter).bindNow();
+	}
+
+	private static void stopServer() {
+		if (httpServer != null) {
+			httpServer.disposeNow();
+		}
+	}
+
+	// ----------------------------------------------------
+	// Transport servers to test
+	// ----------------------------------------------------
+
+	/**
+	 * All transport types we want to test. We use a {@link MethodSource} rather than a
+	 * {@link org.junit.jupiter.params.provider.ValueSource} to provide a readable name.
+	 */
+	static Stream<Arguments> transports() {
+		//@formatter:off
+		return Stream.of(
+				arguments(named("SSE", new Sse())),
+				arguments(named("Streamable HTTP", new StreamableHttp())),
+				arguments(named("Stateless", new Stateless()))
+		);
+		//@formatter:on
+	}
+
+	/**
+	 * Represents a server transport we want to test, and how to create a client for the
+	 * resulting MCP Server.
+	 */
+	interface Transport {
+
+		McpSyncClient createMcpClient(String baseUrl, TestOriginHeaderExchangeFilterFunction customizer);
+
+		RouterFunction<?> routerFunction();
+
+	}
+
+	/**
+	 * SSE-based transport.
+	 */
+	static class Sse implements Transport {
+
+		private final WebFluxSseServerTransportProvider transportProvider;
+
+		public Sse() {
+			transportProvider = WebFluxSseServerTransportProvider.builder()
+				.messageEndpoint("/mcp/message")
+				.securityValidator(
+						DefaultServerTransportSecurityValidator.builder().allowedOrigin("http://localhost:*").build())
+				.build();
+			McpServer.sync(transportProvider)
+				.serverInfo("test-server", "1.0.0")
+				.capabilities(McpSchema.ServerCapabilities.builder().tools(true).build())
+				.build();
+		}
+
+		@Override
+		public McpSyncClient createMcpClient(String baseUrl,
+				TestOriginHeaderExchangeFilterFunction exchangeFilterFunction) {
+			var transport = WebFluxSseClientTransport
+				.builder(WebClient.builder().baseUrl(baseUrl).filter(exchangeFilterFunction))
+				.jsonMapper(McpJsonMapper.getDefault())
+				.build();
+			return McpClient.sync(transport).initializationTimeout(Duration.ofMillis(500)).build();
+		}
+
+		@Override
+		public RouterFunction<?> routerFunction() {
+			return transportProvider.getRouterFunction();
+		}
+
+	}
+
+	static class StreamableHttp implements Transport {
+
+		private final WebFluxStreamableServerTransportProvider transportProvider;
+
+		public StreamableHttp() {
+			transportProvider = WebFluxStreamableServerTransportProvider.builder()
+				.securityValidator(
+						DefaultServerTransportSecurityValidator.builder().allowedOrigin("http://localhost:*").build())
+				.build();
+			McpServer.sync(transportProvider)
+				.serverInfo("test-server", "1.0.0")
+				.capabilities(McpSchema.ServerCapabilities.builder().tools(true).build())
+				.build();
+		}
+
+		@Override
+		public McpSyncClient createMcpClient(String baseUrl,
+				TestOriginHeaderExchangeFilterFunction exchangeFilterFunction) {
+			var transport = WebClientStreamableHttpTransport
+				.builder(WebClient.builder().baseUrl(baseUrl).filter(exchangeFilterFunction))
+				.jsonMapper(McpJsonMapper.getDefault())
+				.openConnectionOnStartup(true)
+				.build();
+			return McpClient.sync(transport).initializationTimeout(Duration.ofMillis(500)).build();
+		}
+
+		@Override
+		public RouterFunction<?> routerFunction() {
+			return transportProvider.getRouterFunction();
+		}
+
+	}
+
+	static class Stateless implements Transport {
+
+		private final WebFluxStatelessServerTransport transportProvider;
+
+		public Stateless() {
+			transportProvider = WebFluxStatelessServerTransport.builder()
+				.securityValidator(
+						DefaultServerTransportSecurityValidator.builder().allowedOrigin("http://localhost:*").build())
+				.build();
+			McpServer.sync(transportProvider)
+				.serverInfo("test-server", "1.0.0")
+				.capabilities(McpSchema.ServerCapabilities.builder().tools(true).build())
+				.build();
+		}
+
+		@Override
+		public McpSyncClient createMcpClient(String baseUrl,
+				TestOriginHeaderExchangeFilterFunction exchangeFilterFunction) {
+			var transport = WebClientStreamableHttpTransport
+				.builder(WebClient.builder().baseUrl(baseUrl).filter(exchangeFilterFunction))
+				.jsonMapper(McpJsonMapper.getDefault())
+				.openConnectionOnStartup(true)
+				.build();
+			return McpClient.sync(transport).initializationTimeout(Duration.ofMillis(500)).build();
+		}
+
+		@Override
+		public RouterFunction<?> routerFunction() {
+			return transportProvider.getRouterFunction();
+		}
+
+	}
+
+	static class TestOriginHeaderExchangeFilterFunction implements ExchangeFilterFunction {
+
+		private String origin = null;
+
+		public void setOriginHeader(String origin) {
+			this.origin = origin;
+		}
+
+		@Override
+		public Mono<ClientResponse> filter(ClientRequest request, ExchangeFunction next) {
+			var updatedRequest = ClientRequest.from(request).header("origin", this.origin).build();
+			return next.exchange(updatedRequest);
+		}
+
+	}
+
+}