Unsupported principal: class org.nuxeo.ecm.platform.usermanager.NuxeoPrincipalImpl

Configure Tomcat to run Nuxeo under an alternative contextPath (change configuration property org.nuxeo.ecm.contextPath and create a new Tomcat Context file).

On attempting log in (after submitting your credentials) you are presented with a simple white page displaying the following message:

If you can read this in your browser, this probably because of a configuration problem of your nuxeo.war/WEB-INF/pages.xml. To change this, edit the OSGI-INF/deployment-fragment.xml of your project at extension pages#PAGES.

And in the server log there is the following stack:

Caused by: java.lang.Error: Unsupported principal: class org.nuxeo.ecm.platform.usermanager.NuxeoPrincipalImpl
at org.nuxeo.ecm.core.api.local.LocalSession.createSession(LocalSession.java:83)
at org.nuxeo.ecm.core.api.local.LocalSession.getSession(LocalSession.java:166)
at org.nuxeo.ecm.core.api.AbstractSession.connect(AbstractSession.java:214)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.nuxeo.ecm.core.api.TransactionalCoreSessionWrapper.invoke(TransactionalCoreSessionWrapper.java:94)
at $Proxy25.connect(Unknown Source)
at org.nuxeo.ecm.core.api.repository.Repository.open(Repository.java:155)
at org.nuxeo.ecm.core.api.repository.Repository.open(Repository.java:113)
at org.nuxeo.ecm.webapp.delegate.DocumentManagerBusinessDelegate.getDocumentManager(DocumentManagerBusinessDelegate.java:113)
... 138 more
2011-05-26 10:38:42,373 ERROR [org.nuxeo.ecm.webapp.delegate.DocumentManagerBusinessDelegate] Unable to login as System
javax.security.auth.login.LoginException: System login failed - callback failed
at org.nuxeo.runtime.api.login.SystemLoginModule.login(SystemLoginModule.java:66)
at org.nuxeo.runtime.api.LoginModuleWrapper.login(LoginModuleWrapper.java:77)

The message is from org.nuxeo.ecm.core.api.local.LocalSession. This is performing an instanceof check for NuxeoPrincipal and failing. The principal is a NuxeoPrincipalImpl which does implements NuxeoPrincipal (a classloader issue?)