Enable HTTP Basic Authentication on a WSO2 Proxy Service - wso2

Question

I have a little problem regarding the use of HTTP Basic Authentication on a WSO2 Proxy, All my service consumers are sending their credentials through HTTP Basic Authentication , & i need to authenticate them on WSO2 Standard user store.
I chose to follow this tutorial , which uses a custom mediator : http://wso2.com/library/knowledge-base/convert-http-basic-authentication-ws-security-username-token/
The problem is when i run a test, i have the following error on WSO2 , apparently the returned user realm is null :
ERROR {org.wso2.carbon.esb.mediator.basicauth.internal.BasicAuthMediatorServiceComponent} - Before activating Carbon Core bundle, an instance of UserRealm service should be in existance {org.wso2.carbon.esb.mediator.basicauth.internal.BasicAuthMediatorServiceComponent}
TID: [0] [ESB] [2015-04-16 16:34:13,684] ERROR {org.wso2.carbon.esb.mediator.basicauth.BasicAuthWSSecMediator} - Could not authenticate user :: WSO2_Portail. Error is Before activating Carbon Core bundle, an instance of UserRealm service should be in existance {org.wso2.carbon.esb.mediator.basicauth.BasicAuthWSSecMediator}
java.lang.Exception: Before activating Carbon Core bundle, an instance of UserRealm service should be in existance
at org.wso2.carbon.esb.mediator.basicauth.internal.BasicAuthMediatorServiceComponent.getUserRealm(BasicAuthMediatorServiceComponent.java:41)
at org.wso2.carbon.esb.mediator.basicauth.BasicAuthWSSecMediator.isAuthenticated(BasicAuthWSSecMediator.java:186)
at org.wso2.carbon.esb.mediator.basicauth.BasicAuthWSSecMediator.mediate(BasicAuthWSSecMediator.java:102)
at org.apache.synapse.mediators.ext.ClassMediator.mediate(ClassMediator.java:78)
at org.apache.synapse.mediators.AbstractListMediator.mediate(AbstractListMediator.java:77)
at org.apache.synapse.mediators.AbstractListMediator.mediate(AbstractListMediator.java:47)
at org.apache.synapse.mediators.base.SequenceMediator.mediate(SequenceMediator.java:131)
at org.apache.synapse.core.axis2.ProxyServiceMessageReceiver.receive(ProxyServiceMessageReceiver.java:166)
at org.apache.axis2.engine.AxisEngine.receive(AxisEngine.java:180)
at org.apache.synapse.transport.passthru.ServerWorker.processEntityEnclosingRequest(ServerWorker.java:411)
at org.apache.synapse.transport.passthru.ServerWorker.run(ServerWorker.java:183)
at org.apache.axis2.transport.base.threads.NativeWorkerPool$1.run(NativeWorkerPool.java:172)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)