Authenticator: synchronize on the instance, rather than the userMap
Authenticator: synchronize on the instance, rather than the userMap

The userMap can change, so it makes more sense to synchronize on an
unchanging object

Fierozen/owasp-esapi-java,Fierozen/owasp-esapi-java,Fierozen/owasp-esapi-java,ibnemahdi/owasp-esapi-java,ibnemahdi/owasp-esapi-java,ibnemahdi/owasp-esapi-java