23. WebSocket Security
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## 23. WebSocket Security

Spring Security 4 added support for securing Spring’s WebSocket support. This section describes how to use Spring Security’s WebSocket support.

| Note
You can find a complete working sample of WebSocket security in samples/javaconfig/chat.

## 23.1 WebSocket Configuration

Spring Security 4.0 has introduced authorization support for WebSockets through the Spring Messaging abstraction. To configure authorization using Java Configuration, simply extend the `AbstractSecurityWebSocketMessageBrokerConfigurer` and configure the `MessageSecurityMetadataSourceRegistry`. For example:

    @Configuration
    public class WebSocketSecurityConfig
          extends AbstractSecurityWebSocketMessageBrokerConfigurer {

        protected void configureInbound(MessageSecurityMetadataSourceRegistry messages) {
            messages
                    .simpDestMatchers("/user/*").authenticated()
        }
    }

This will ensure that:

| Any inbound CONNECT message requires a valid CSRF token to enforce Same Origin Policy
| The SecurityContextHolder is populated with the user within the simpUser header attribute for any inbound request.
| Our messages require the proper authorization. Specifically, any inbound message that starts with "/user/" will require ROLE_USER. Additional details on authorization can be found in Section 23.3, “WebSocket Authorization”

Spring Security also provides XML Namespace support for securing WebSockets. A comparable XML based configuration looks like the following:

    <websocket-message-broker>

        <intercept-message pattern="/user/**" access="hasRole('USER')" />
    </websocket-message-broker>

This will ensure that:

| Any inbound CONNECT message requires a valid CSRF token to enforce Same Origin Policy
| The SecurityContextHolder is populated with the user within the simpUser header attribute for any inbound request.
| Our messages require the proper authorization. Specifically, any inbound message that starts with "/user/" will require ROLE_USER. Additional details on authorization can be found in Section 23.3, “WebSocket Authorization”

## 23.2 WebSocket Authentication

WebSockets reuse the same authentication information that is found in the HTTP request when the WebSocket connection was made. This means that the `Principal` on the `HttpServletRequest` will be handed off to WebSockets. If you are using Spring Security, the `Principal` on the `HttpServletRequest` is overridden automatically.

More concretely, to ensure a user has authenticated to your WebSocket application, all that is necessary is to ensure that you setup Spring Security to authenticate your HTTP based web application.

## 23.3 WebSocket Authorization

Spring Security 4.0 has introduced authorization support for WebSockets through the Spring Messaging abstraction. To configure authorization using Java Configuration, simply extend the `AbstractSecurityWebSocketMessageBrokerConfigurer` and configure the `MessageSecurityMetadataSourceRegistry`. For example:

    @Configuration
    public class WebSocketSecurityConfig extends AbstractSecurityWebSocketMessageBrokerConfigurer {

        @Override
        protected void configureInbound(MessageSecurityMetadataSourceRegistry messages) {
            messages
                    .nullDestMatcher().authenticated()
                    .simpSubscribeDestMatchers("/user/queue/errors").permitAll()
                    .simpDestMatchers("/app/**").hasRole("USER")
                    .simpSubscribeDestMatchers("/user/**", "/topic/friends/*").hasRole("USER")
                    .simpTypeMatchers(MESSAGE, SUBSCRIBE).denyAll()
                    .anyMessage().denyAll();

        }
    }

This will ensure that:

| Any message without a destination (i.e. anything other than Message type of MESSAGE or SUBSCRIBE) will require the user to be authenticated
| Anyone can subscribe to /user/queue/errors
| Any message that has a destination starting with "/app/" will be require the user to have the role ROLE_USER
| Any message that starts with "/user/" or "/topic/friends/" that is of type SUBSCRIBE will require ROLE_USER
| Any other message of type MESSAGE or SUBSCRIBE is rejected. Due to 6 we do not need this step, but it illustrates how one can match on specific message types.
| Any other Message is rejected. This is a good idea to ensure that you do not miss any messages.

Spring Security also provides XML Namespace support for securing WebSockets. A comparable XML based configuration looks like the following:

    <websocket-message-broker>

        <intercept-message type="CONNECT" access="permitAll" />
        <intercept-message type="UNSUBSCRIBE" access="permitAll" />
        <intercept-message type="DISCONNECT" access="permitAll" />

        <intercept-message pattern="/user/queue/errors" type="SUBSCRIBE" access="permitAll" />
        <intercept-message pattern="/app/**" access="hasRole('USER')" />

        <intercept-message pattern="/user/**" access="hasRole('USER')" />
        <intercept-message pattern="/topic/friends/*" access="hasRole('USER')" />

        <intercept-message type="MESSAGE" access="denyAll" />
        <intercept-message type="SUBSCRIBE" access="denyAll" />

        <intercept-message pattern="/**" access="denyAll" />
    </websocket-message-broker>

This will ensure that:

| Any message of type CONNECT, UNSUBSCRIBE, or DISCONNECT will require the user to be authenticated
| Anyone can subscribe to /user/queue/errors
| Any message that has a destination starting with "/app/" will be require the user to have the role ROLE_USER
| Any message that starts with "/user/" or "/topic/friends/" that is of type SUBSCRIBE will require ROLE_USER
| Any other message of type MESSAGE or SUBSCRIBE is rejected. Due to 6 we do not need this step, but it illustrates how one can match on specific message types.
| Any other message with a destination is rejected. This is a good idea to ensure that you do not miss any messages.

### 23.3.1 WebSocket Authorization Notes

In order to properly secure your application it is important to understand Spring’s WebSocket support.

#### WebSocket Authorization on Message Types

It is important to understand the distinction between SUBSCRIBE and MESSAGE types of messages and how it works within Spring.

Consider a chat application.

- The system can send notifications MESSAGE to all users through a destination of "/topic/system/notifications"
- Clients can receive notifications by SUBSCRIBE to the "/topic/system/notifications".

While we want clients to be able to SUBSCRIBE to "/topic/system/notifications", we do not want to enable them to send a MESSAGE to that destination. If we allowed sending a MESSAGE to "/topic/system/notifications", then clients could send a message directly to that endpoint and impersonate the system.

In general, it is common for applications to deny any MESSAGE sent to a message that starts with the broker prefix (i.e. "/topic/" or "/queue/").

#### WebSocket Authorization on Destinations

It is also is important to understand how destinations are transformed.

Consider a chat application.

- Users can send messages to a specific user by sending a message to the destination of "/app/chat".
- The application sees the message, ensures that the "from" attribute is specified as the current user (we cannot trust the client).
- The application then sends the message to the recipient using `SimpMessageSendingOperations.convertAndSendToUser("toUser", "/queue/messages", message)`.
- The message gets turned into the destination of "/queue/user/messages-<sessionid>"

With the application above, we want to allow our client to listen to "/user/queue" which is transformed into "/queue/user/messages-<sessionid>". However, we do not want the client to be able to listen to "/queue/*" because that would allow the client to see messages for every user.

In general, it is common for applications to deny any SUBSCRIBE sent to a message that starts with the broker prefix (i.e. "/topic/" or "/queue/"). Of course we may provide exceptions to account for things like

### 23.3.2 Outbound Messages

Spring contains a section titled Flow of Messages that describes how messages flow through the system. It is important to note that Spring Security only secures the `clientInboundChannel`. Spring Security does not attempt to secure the `clientOutboundChannel`.

The most important reason for this is performance. For every message that goes in, there are typically many more that go out. Instead of securing the outbound messages, we encourage securing the subscription to the endpoints.

## 23.4 Enforcing Same Origin Policy

It is important to emphasize that the browser does not enforce the Same Origin Policy for WebSocket connections. This is an extremely important consideration.

### 23.4.1 Why Same Origin?

Consider the following scenario. A user visits bank.com and authenticates to their account. The same user opens another tab in their browser and visits evil.com. The Same Origin Policy ensures that evil.com cannot read or write data to bank.com.

With WebSockets the Same Origin Policy does not apply. In fact, unless bank.com explicitly forbids it, evil.com can read and write data on behalf of the user. This means that anything the user can do over the webSocket (i.e. transfer money), evil.com can do on that users behalf.

Since SockJS tries to emulate WebSockets it also bypasses the Same Origin Policy. This means developers need to explicitly protect their applications from external domains when using SockJS.

### 23.4.2 Spring WebSocket Allowed Origin

Fortunately, since Spring 4.1.5 Spring’s WebSocket and SockJS support restricts access to the current domain. Spring Security adds an additional layer of protection to provide defence in depth.

### 23.4.3 Adding CSRF to Stomp Headers

By default Spring Security requires the CSRF token in any CONNECT message type. This ensures that only a site that has access to the CSRF token can connect. Since only the Same Origin can access the CSRF token, external domains are not allowed to make a connection.

Typically we need to include the CSRF token in an HTTP header or an HTTP parameter. However, SockJS does not allow for these options. Instead, we must include the token in the Stomp headers

Applications can obtain a CSRF token by accessing the request attribute named _csrf. For example, the following will allow accessing the `CsrfToken` in a JSP:

    var headerName = "${_csrf.headerName}";
    var token = "${_csrf.token}";

If you are using static HTML, you can expose the `CsrfToken` on a REST endpoint. For example, the following would expose the `CsrfToken` on the URL /csrf

    @RestController
    public class CsrfController {

        @RequestMapping("/csrf")
        public CsrfToken csrf(CsrfToken token) {
            return token;
        }
    }

The JavaScript can make a REST call to the endpoint and use the response to populate the headerName and the token.

We can now include the token in our Stomp client. For example:

    ...
    var headers = {};
    headers[headerName] = token;
    stompClient.connect(headers, function(frame) {
      ...

    }

### 23.4.4 Disable CSRF within WebSockets

If you want to allow other domains to access your site, you can disable Spring Security’s protection. For example, in Java Configuration you can use the following:

    @Configuration
    public class WebSocketSecurityConfig extends AbstractSecurityWebSocketMessageBrokerConfigurer {

        ...

        @Override
        protected boolean sameOriginDisabled() {
            return true;
        }
    }

## 23.5 Working with SockJS

SockJS provides fallback transports to support older browsers. When using the fallback options we need to relax a few security constraints to allow SockJS to work with Spring Security.

### 23.5.1 SockJS & frame-options

SockJS may use an transport that leverages an iframe. By default Spring Security will deny the site from being framed to prevent Clickjacking attacks. To allow SockJS frame based transports to work, we need to configure Spring Security to allow the same origin to frame the content.

You can customize X-Frame-Options with the frame-options element. For example, the following will instruct Spring Security to use "X-Frame-Options: SAMEORIGIN" which allows iframes within the same domain:

    <http>
        <!-- ... -->

        <headers>
            <frame-options
              policy="SAMEORIGIN" />
        </headers>
    </http>

Similarly, you can customize frame options to use the same origin within Java Configuration using the following:

    @EnableWebSecurity
    public class WebSecurityConfig extends
       WebSecurityConfigurerAdapter {

      @Override
      protected void configure(HttpSecurity http) throws Exception {
        http
          // ...
          .headers()
            .frameOptions()
                .sameOrigin();
      }
    }

### 23.5.2 SockJS & Relaxing CSRF

SockJS uses a POST on the CONNECT messages for any HTTP based transport. Typically we need to include the CSRF token in an HTTP header or an HTTP parameter. However, SockJS does not allow for these options. Instead, we must include the token in the Stomp headers as described in Section 23.4.3, “Adding CSRF to Stomp Headers”.

It also means we need to relax our CSRF protection with the web layer. Specifically, we want to disable CSRF protection for our connect URLs. We do NOT want to disable CSRF protection for every URL. Otherwise our site will be vulnerable to CSRF attacks.

We can easily achieve this by providing a CSRF RequestMatcher. Our Java Configuration makes this extremely easy. For example, if our stomp endpoint is "/chat" we can disable CSRF protection for only URLs that start with "/chat/" using the following configuration:

    @Configuration
    @EnableWebSecurity
    public class WebSecurityConfig
        extends WebSecurityConfigurerAdapter {

        @Override
        protected void configure(HttpSecurity http) throws Exception {

            http
                .csrf()
                    // ignore our stomp endpoints since they are protected using Stomp headers
                    .ignoringAntMatchers("/chat/**")
                    .and()
                .headers()
                    // allow same origin to frame our site to support iframe SockJS
                    .frameOptions().sameOrigin()
                    .and()
                .authorizeRequests()

                ...

If we are using XML based configuration, we can use the csrf@request-matcher-ref. For example:

    <http ...>
        <csrf request-matcher-ref="csrfMatcher"/>

        <headers>
            <frame-options policy="SAMEORIGIN"/>
        </headers>

        ...
    </http>

    <b:bean id="csrfMatcher"
        class="AndRequestMatcher">
        <b:constructor-arg value="#{T(org.springframework.security.web.csrf.CsrfFilter).DEFAULT_CSRF_MATCHER}"/>
        <b:constructor-arg>
            <b:bean class="org.springframework.security.web.util.matcher.NegatedRequestMatcher">
              <b:bean class="org.springframework.security.web.util.matcher.AntPathRequestMatcher">
                <b:constructor-arg value="/chat/**"/>
              </b:bean>
            </b:bean>
        </b:constructor-arg>
    </b:bean>

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