LDAP implementation of UserDetailsService based around an LdapUserSearch
and an LdapAuthoritiesPopulator. The final UserDetails object
returned from loadUserByUsername is created by the configured UserDetailsContextMapper.
Locates the user based on the username. In the actual implementation, the search may possibly be case
sensitive, or case insensitive depending on how the implementation instance is configured. In this case, the
UserDetails object that comes back may have a username that is of a different case than what was