WSO2IS NullPointerException when using step authenticator - saml

Question

Occasionally (?) the WSO2 IS user is unable to authenticate with following exception. When retrying, the user will be authenticated. Any ideas what could be reason / resolution? We set up the session caching.
Using WSO2 Identity Server 5.0.0.SP1 / SAML authentication with the authenticator set to advanced (single step, multiple options). I cannot find the correct source code commit to check out (to match the line number in the exception)
Thank you all in advance
Gabriel
TID: [0] [IS] [2016-02-15 13:07:22,914] ERROR
{org.wso2.carbon.identity.application.authentication.framework.handler.request.impl.DefaultRequestCoordinator}
- Exception in Authentication Framework {org.wso2.carbon.identity.application.authentication.framework.handler.request.impl.DefaultRequestCoordinator}
java.lang.NullPointerException at
org.wso2.carbon.identity.application.authentication.framework.handler.sequence.impl.DefaultStepBasedSequenceHandler.handle(DefaultStepBasedSequenceHandler.java:83)
at
org.wso2.carbon.identity.application.authentication.framework.handler.request.impl.DefaultAuthenticationRequestHandler.handle(DefaultAuthenticationRequestHandler.java:121)
at
org.wso2.carbon.identity.application.authentication.framework.handler.request.impl.DefaultRequestCoordinator.handle(DefaultRequestCoordinator.java:94)
at
org.wso2.carbon.identity.application.authentication.framework.servlet.CommonAuthenticationServlet.doPost(CommonAuthenticationServlet.java:54)
at
org.wso2.carbon.identity.application.authentication.framework.servlet.CommonAuthenticationServlet.doGet(CommonAuthenticationServlet.java:44)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:735) at
javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
Edit:
This exception occurs on the WSO2 IS 5.1.0 too
see the Source code line 105
StepConfig stepConfig = context.getSequenceConfig().getStepMap().get(currentStep);
// if the current step is completed
if (stepConfig.isCompleted()) {
stepConfig.setCompleted(false);
ERROR org.wso2.carbon.identity.application.authentication.framework.handler.request.impl.DefaultRequestCoordinator} - Exception in Authentication Framework
java.lang.NullPointerException
at org.wso2.carbon.identity.application.authentication.framework.handler.sequence.impl.DefaultStepBasedSequenceHandler.handle(DefaultStepBasedSequenceHandler.java:105)
at org.wso2.carbon.identity.application.authentication.framework.handler.request.impl.DefaultAuthenticationRequestHandler.handle(DefaultAuthenticationRequestHandler.java:115)
it looks like the stepConfig 'dissapeared' from the authentication config. The setup is done on a single node with session persistence into a database.

Answer 1

Apparently it looks like a problem with concurrency.
When multiple concurrent requests are sent to the SSO endpoint while the user is already authenticated, all threads are attempting to process the request modifying the same authentication context object (currentStep counter) so the cached authentication context comes to an invalid state.
Valid use case is that the client should send only a single request to the SSO endpoint, so the team dealing with the UI have to fix it. But - that's only the a quick fix not preventing the issue in long term. We have to really pick it up with WSO2 (and fix the code ourselves maybe) :)
g.