The following 3 sections of code combine to cause a StackOverflowError...

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// RemoteUserPersonManager.java @line 54...

        // If the user has authenticated with the server which has implemented web authentication,
        // the REMOTE_USER environment variable will be set.
        String remoteUser = request.getRemoteUser();

// PortalHttpServletRequest.java

    public String getRemoteUser() {
        final Principal userPrincipal = this.getUserPrincipal();
        if (userPrincipal == null) {
            return null;
        }
 
        return userPrincipal.getName();
    }
 
[...]

    public Principal getUserPrincipal() {
        final IPerson person = this.personManager.getPerson(this);
        if (person == null || person.isGuest()) {
            return null;
        }
       
        return person;
    }