Character encoding with cfntauthenticate

I've been authenticating users of my web app against Active Directory using the cfntauthenticate tag which works pretty well and was simple to implement.  We have one or two European users who cannot log in because they are getting an invalid password error.  There username and password was checked as being valid by using other non-CFapplications that also authenticate against the domain .  The common thread seems to be that they use umlauted or other European accented characters.  These characters can be multi-byte in a unicode environment so I've tried a number of methods to altering the encoding of the page so that the password is recognized as valid but have had no luck so far.  Has anyone encountered this or have any information on the encoding of the form field when passing it through this tag? 

Brian