MCP server: Authentication lost in tool execution

[GregoireW]

Bug description

I'm in a situation where I have authentication with OIDC (so an access token basically).

When I set authentication required on the /sse and /mcp/** endpoint, then the client side only connect when I provide the correct access token. This is ok.

Even when the client send a call to a tool, the authentication is needed, but inside the executed code, I cannot access the authentication.

SecurityContextHolder.getContext().getAuthentication() and ReactiveSecurityContextHolder.getContext() return null.

Long story short, I cannot control data ownership so this is bad, and my MCP server also execute some api call that need to be authenticated, and I use the oauth2ClientRequestInterceptor to do token exchange so this also fail. ( the MCP core even with SYNC option goes through reactive code and the original servlet thread is put on hold, giving the execution to a 'boundedElactic' thread )

Environment

Spring MVC ( springboot 3.4 )
Spring AI 1.0.0-M6 ( spring-ai-mcp-server-webmvc-spring-boot-starter )
spring-boot-starter-oauth2-resource-server (for oauth2 authentication )

Steps to reproduce

Enable authentication on an application, create a Tool that just return the authenticated user.

Expected behavior

I expect to be able to find the security context when a tool is called from MCP

Minimal Complete Reproducible example

Enable authentication on a springboot with MCP server activated,
Create a Tool

@Tool(description="Get your name")
    public String getYourName() {
        return SecurityContextHolder.getContext().getAuthentication().getName();
    }

call the tool. It should answer your sub and not null.

[jochenchrist]

Same issue here. This is a major blocker for any remote server application that relies on authentication.

[emdzej]

I had similar issue, and had a quick look at the implementation (for 1.0.0-M6 and respective dependency versions)

For this to work, the mono chain needs to be preserved through out the entire chain. Having a brief look, it seems that the implementation of the io.modelcontextprotocol.spec.DefaultMcpSession is not right for webflux.

Seems it's not spring-ai issue.

After changing the implementation in io.modelcontextprotocol.spec.DefaultMcpSession slighlty:

public DefaultMcpSession(Duration requestTimeout, McpTransport transport,
						  Map<String, RequestHandler<?>> requestHandlers, Map<String, NotificationHandler> notificationHandlers) {

		Assert.notNull(requestTimeout, "The requstTimeout can not be null");
		Assert.notNull(transport, "The transport can not be null");
		Assert.notNull(requestHandlers, "The requestHandlers can not be null");
		Assert.notNull(notificationHandlers, "The notificationHandlers can not be null");

		this.requestTimeout = requestTimeout;
		this.transport = transport;
		this.requestHandlers.putAll(requestHandlers);
		this.notificationHandlers.putAll(notificationHandlers);

		// TODO: consider mono.transformDeferredContextual where the Context contains
		// the
		// Observation associated with the individual message - it can be used to
		// create child Observation and emit it together with the message to the
		// consumer
		this.connection = this.transport.connect(
				mono -> mono.flatMap(message -> {
					if (message instanceof McpSchema.JSONRPCResponse response) {
						logger.debug("Received Response: {}", response);
						var sink = pendingResponses.remove(response.id());
						if (sink == null) {
							logger.warn("Unexpected response for unkown id {}", response.id());
						}
						else {
							sink.success(response);
						}
						return Mono.just(message);
					}
					else if (message instanceof McpSchema.JSONRPCRequest request) {
						logger.debug("Received request: {}", request);
						return handleIncomingRequest(request).flatMap(transport::sendMessage).onErrorResume(
								error -> {
									var errorResponse = new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(),
											null, new McpSchema.JSONRPCResponse.JSONRPCError(
											McpSchema.ErrorCodes.INTERNAL_ERROR, error.getMessage(), null));
									return transport.sendMessage(errorResponse);
								}).thenReturn(message);
					}
					else if (message instanceof McpSchema.JSONRPCNotification notification) {
						logger.debug("Received notification: {}", notification);
						return handleIncomingNotification(notification).thenReturn(message);
					}
					return Mono.just(message);
				})

		).subscribe();
	}

SecurityContext is preserved.

The main issue in the original implementation is the subscription to the handler that is being done instead of chaining the response with the request:

else if (message instanceof McpSchema.JSONRPCRequest request) {
				logger.debug("Received request: {}", request);
				handleIncomingRequest(request).subscribe(response -> transport.sendMessage(response).subscribe(),
						error -> {
							var errorResponse = new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(),
									null, new McpSchema.JSONRPCResponse.JSONRPCError(
											McpSchema.ErrorCodes.INTERNAL_ERROR, error.getMessage(), null));
							transport.sendMessage(errorResponse).subscribe();
						});
			}

[emdzej]

@GregoireW please also note that despite fixing the issue as above, the @Tool registration will not work, since it's not correctly handled in asynchronous scenario. I did not dig too deep tho.

I had to create registrations by hand

    @Bean
    public List<McpServerFeatures.AsyncToolRegistration> tools(TaskService taskService,
                                                               ObjectMapper objectMapper) {

        return List.of(
                new McpServerFeatures.AsyncToolRegistration(
                        new McpSchema.Tool("tasks", "tasks", "{\n" +
                                "  \"$schema\": \"http://json-schema.org/draft-07/schema#\",\n" +
                                "  \"$id\": \"file://schemas/simple.schema.json\",\n" +
                                "  \"title\": \"simplified data\",\n" +
                                "  \"description\": \"simple\",\n" +
                                "  \"type\": \"object\",\n" +
                                "  \"properties\": {\n" +
                                "    }\n" +
                                "  }}"),
                        (request) -> {
                            return taskService.getCurrentUserTasks()
                                    .map(task -> {
                                        try {
                                            return new McpSchema.TextContent(
                                                    objectMapper.writeValueAsString(task)
                                            );
                                        } catch (JsonProcessingException e) {
                                            throw new RuntimeException(e);
                                        }
                                    })
                                    .cast(McpSchema.Content.class)
                                    .collectList()
                                    .flatMap(i -> Mono.just(new McpSchema.CallToolResult(i, false)));
                        }
                )
        );
    }

[GregoireW]

@emdzej Thanks for the heads up and for drilling a little bit more on that (I did not took a deep dive in this subject and did something else for my use case) Next time I will know what to check

[emdzej]

Looks like this has been fixed in mcp java-sdk 0.8.x https://github.com/modelcontextprotocol/java-sdk/blob/0.8.x/mcp/src/main/java/io/modelcontextprotocol/spec/McpServerSession.java

So... hopefully with next release will be covered :)

[GregoireW]

Wonderful news!

[los-ko]

Doesnt seem to be working on snapshot yet, even tho it has mcp java-sdk 0.8.x.

[emdzej]

@los-ko have you tried with the tool annotation or manual registration?
If no other changes were made the annotation will not work to the best of my knowledge, since it's not reactive.

[los-ko]

We have only tried with the tool annotation.

[poo0054]

Hi, if I don't use Security, is there any other way for me to get the current header or specified parameters?
similar #2757

[djcrabhat]

Was surprised by this today, too. In my dreams, "@AuthenticationPrincipal" could work just like it does on a controller, giving me access to the JWT that the Spring Security stack has already negotiated for me. But even getting the Authentication directly from the SecurityContext is a no-go.

[eric-eldard]

Seems I'm experiencing this issue too. I'm running an McpSyncServer, but it just delegates everything to McpAsyncServer (creating a new thread, then blocking on the result), and the security context is fumbled in the handoff. Needed a quick workaround until this gets patched, so...father forgive me for this one...

@Getter
public class AuthAwareMcpServerSession extends McpServerSession
{
    private final Authentication authentication;

    public AuthAwareMcpServerSession(Authentication authentication, String id, Duration requestTimeout,
                                     McpServerTransport transport, InitRequestHandler initHandler,
                                     InitNotificationHandler initNotificationHandler,
                                     Map<String, RequestHandler<?>> requestHandlers,
                                     Map<String, NotificationHandler> notificationHandlers
    )
    {
        super(id, requestTimeout, transport, initHandler, initNotificationHandler, requestHandlers, notificationHandlers);
        this.authentication = authentication;
    }
}

@Configuration
public class McpConfig
{
    @Bean
    public ToolCallbackProvider tools(...)
    {
        return ToolCallbackProvider.from(ToolCallbacks.from(...));
    }

    @Bean
    public WebMvcSseServerTransportProvider mcpServerTransportProvider(McpServerProperties serverProperties,
                                                                       ObjectProvider<ObjectMapper> objectMapperProvider)
    {
        return new WebMvcSseServerTransportProvider(
            objectMapperProvider.getIfAvailable(ObjectMapper::new),
            serverProperties.getBaseUrl(),
            serverProperties.getSseMessageEndpoint(),
            serverProperties.getSseEndpoint()
        )
        {
            @Override
            public void setSessionFactory(McpServerSession.Factory sessionFactory)
            {
                McpServerSession template = sessionFactory.create(null);

                super.setSessionFactory(transport -> new AuthAwareMcpServerSession(
                    SecurityContextHolder.getContext().getAuthentication(), // auth goes in
                    UUID.randomUUID().toString(),
                    ReflectionUtils.getFieldValue(template, "requestTimeout", Duration.class), // avert your eyes
                    transport,
                    ReflectionUtils.getFieldValue(template, "initRequestHandler", McpServerSession.InitRequestHandler.class),
                    Mono::empty,
                    ReflectionUtils.getFieldValue(template, "requestHandlers", Map.class),
                    ReflectionUtils.getFieldValue(template, "notificationHandlers", Map.class)
                ));
            }
        };
    }

    @Bean
    public RouterFunction<ServerResponse> mvcMcpRouterFunction(WebMvcSseServerTransportProvider transportProvider)
    {
        return transportProvider.getRouterFunction();
    }
}

@Slf4j
@Aspect
@Component
public class ToolAuthAdvice
{
    @Around("@annotation(org.springframework.ai.tool.annotation.Tool)")
    public Object wrapToolInvocation(ProceedingJoinPoint joinPoint) throws Throwable
    {
        ToolContext toolContext = ReflectionUtils.getArgValue(joinPoint, ToolContext.class); // it's magic
        if (toolContext == null)
        {
            log.debug("No context for method annotated with @Tool; executing tool without authentication");
            return joinPoint.proceed();
        }

        McpSyncServerExchange syncExchange = (McpSyncServerExchange) toolContext.getContext().get("exchange");
        Preconditions.checkNotNull(syncExchange, "No sync exchange found in tool context");

        McpAsyncServerExchange asyncExchange = ReflectionUtils.getFieldValue(syncExchange, "exchange", McpAsyncServerExchange.class);
        Preconditions.checkNotNull(asyncExchange, "No async exchange found in sync exchange");

        McpServerSession session = ReflectionUtils.getFieldValue(asyncExchange, "session", McpServerSession.class);
        Preconditions.checkNotNull(session, "No session found in async exchange");

        if (session instanceof AuthAwareMcpServerSession authAwareSession)
        {
            try
            {
                Authentication authentication = authAwareSession.getAuthentication() // auth comes out

                // You may wish to revalidate the authentication here, for this request, since it was added at session creation

                SecurityContextHolder.getContext().setAuthentication(authentication)
                return joinPoint.proceed();
            }
            finally
            {
                SecurityContextHolder.clearContext();
            }
        }
        else
        {
            throw new IllegalArgumentException("Cannot proceed; session is not auth-aware");
        }
    }
}

If this was helpful to you, great! If not, I was never here.

[mmengLong]

https://stackoverflow.com/questions/42341635/spring-security-current-user-in-thread

    @PostConstruct
    void setGlobalSecurityContext() {
        SecurityContextHolder.setStrategyName(SecurityContextHolder.MODE_INHERITABLETHREADLOCAL);
    }

works well for WebMVC

[coderliguoqing]

@mmengLong Oh, that's great, it doesn't seem to have anything to do with SpringAi MCP, it's just that we don't know enough about the capabilities of Spring Security's SecurityContextHolder support to solve the problem perfectly; thk.