This happens every couple of months for me. We have several clients that would like to be able to comment or approve documents, but do not want a login to Workfront. Every so often, a client will report that they're being asked for a login and don't want it. I believe what they are doing is clicking one of the many other links in the notification email, such as to a task or project, or the "See it in Workfront" link. Worse, once they click it I believe they get a cookie that redirects them to the login every time they click the email after that. Its frustrating for me and for our clients every time this happens.
It seems to me that if we enter an email address to approve a document, Workfront knows if that is a user or not, and if not it should not include links to things they would need to log in to see.
Telling the client to be careful to only click the document name, or to clear their cookies to stop being redirected to the login screen irritates them since they were told this would be an easy, seamless experience for them. Some of them simply do not understand how to clear cookies, others are annoyed they're being asked to do something outside of what we originally asked them to do: click the link and approve the document.