[squid-users] Whitespaces in username

[Job]

Hello,
 
i am using Squid 3.1.8 with NTLM authentication.
 
I have Windows username with whitespace, as example "Mark Brown".
 
The only way to make this user authenticated is putting the username "Mark 
Brown" into a file:
 
acl Mark proxy_auth "/tmp/mark.txt"
 
and inside /tmp/mark.txt i wrote: Mark Brown
 
Is there a way to specify the username with whitespaces directly in squid.conf?
Thank you!
Francesco