Spring Security: How to get the originally thrown exception of a failed XwsSecurityInterceptor.validateMessage call - spring

Question

My application is using Spring Security to validate incoming Endpoint calls. I am trying to give the client specific error codes when anything goes wrong within the XwsSecurityInterceptor but I haven't yet found a way to do this.
This is what I have tried: I am using an EndpointInterceptor that inherits from XwsSecurityInterceptor:
<bean name="myInterceptor" id="myInterceptor" class="x.y.MyPreAuthenticationSecurityInterceptor">
<property name="policyConfiguration" value="classpath:/security.xml" />
<property name="callbackHandlers">
<list>
<bean id="myCallbackHandler" class="x.y.MyCallbackHandler" />
</list>
</property>
</bean>
The interceptor has a CallbackHandler 'myCallbackHandler' that handles PasswordValidationCallbacks. For testing purposes for each callback it attaches a validator that will instantly throw a certain exception (CustomException) with a certain error code:
#Override
protected void handleInternal(Callback callback) throws IOException, UnsupportedCallbackException {
if (callback instanceof PasswordValidationCallback) {
PasswordValidationCallback validationCallback = (PasswordValidationCallback) callback;
if (validationCallback.getRequest() instanceof PasswordValidationCallback.PlainTextPasswordRequest) {
validationCallback.setValidator(new MyValidator());
return;
}
} else if (callback instanceof CleanupCallback) {
SecurityContextHolder.clearContext();
return;
}
throw new UnsupportedCallbackException(callback);
}
private class MyValidator implements PasswordValidationCallback.PasswordValidator {
public boolean validate(PasswordValidationCallback.Request request) throws PasswordValidationCallback.PasswordValidationException
{
throw new PasswordValidationCallback.PasswordValidationException("test", new CustomException("some error code"));
}
}
As specified in https://docs.spring.io/spring-ws/site/reference/html/security.html, section 7.2.5 the exception handling is done in the handleValidationException method.
In 'MyPreAuthenticationSecurityInterceptor' I am overriding the handleValidationException method:
#Override
public boolean handleValidationException(WsSecurityValidationException ex, MessageContext messageContext) {
if (logger.isWarnEnabled()) {
logger.warn("Could not validate request: " + ex.getMessage());
}
return false;
}
Problem is that when debugging I can't find my CustomException in WsSecurityValidationException. The root cause of is 'com.sun.xml.wss.XWSSecurityException: Invalid Username Password Pair'.
Am I going about this the wrong way?