Some users experience authentication failure when using Microsoft Internet Explorer 11.

The authentication failure could be caused by a user-agent string that changed since Internet Explorer 10. To verify if this is the case, perform a policy trace.

The user-agent string for Internet Explorer 11 is shorter than in previous versions:

Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv 11.0) like Gecko 

The Internet Explorer 10 user-agent string (on Windows 7) is as follows: 

IE10 ::Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; WOW64; Trident/6.0) 

For more information, see http://www.nczonline.net/blog/2013/07/02/internet-explorer-11-dont-call-me-ie/.
 

If the user authenticates using user-agent, use the following regex:

request.header.User-Agent="IE|Firefox|Mozilla"

The following regex works for Internet Explorer 10 but not 11:

request.header.User-Agent="IE|Firefox"