Failed to serialize org.hippoecm.frontend.model.UserCredentials

When logging in to the cms (version 7.9.0 enterprise) running in resin 4 free version we get the following stack trace and are unable to proceed anyfurther.

This exception happens when the servlet container tries to store HttpSession data which is a standard behavior of JEE servlet container.
Therefore, if org.hippoecm.frontend.model.UserCredentials needs to be managed in HttpSession, then it should implement Serializable.

[15:06:29.072]

{resin-port-11120-31} SessionImpl[F97A96E569406912F900D290432CF32B,/cms]: failed storing persistent session attribute 'Wicket:SessionUnbindingListener-CMS'. Persistent session values must extend java.io.Serializable.
java.io.NotSerializableException: org.hippoecm.frontend.model.UserCredentials
[15:06:29.072] {resin-port-11120-31}

SessionImpl[F97A96E569406912F900D290432CF32B,/cms]: can't serialize session
java.io.NotSerializableException: org.hippoecm.frontend.model.UserCredentials
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1180)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
at com.caucho.server.session.JavaSessionSerializer.writeObject(JavaSessionSerializer.java:70)
at com.caucho.server.session.SessionImpl.store(SessionImpl.java:1038)
at com.caucho.server.session.SessionImpl.save(SessionImpl.java:894)
...