I am using the Magento shopping cart, and 99% of my duplicate content errors come from the login page.  The URL looks like: http://www.site.com/customer/account/login/referer/aHR0cDovL3d3dy5tbW1zcGVjaW9zYS5jb20vcmV2aWV3L3Byb2R1Y3QvbGlzdC9pZC8xOTYvY2F0ZWdvcnkvNC8jcmV2aWV3LWZvcm0%2C/ Or, the same url but with the long string different from the one above.  This link is available at the top of every page in my site, but I have made sure to add "rel=nofollow" as an attribute to the link in every case (it is done easily by modifying the header links template). Is there something else I should be doing?  Do I need to try to add canonical to the login page?  If so, does anyone know how to do it using XML?