squid proxy: How to assign different userids to different ACLs?

Question

I am trying to restrict access to certain sites to different user id(s) per site.

An illustration of this would be: site1 may only be accessed from a given source IP and with a specific set of credentials, while site2 will be permitted to be accessed from a different source IP and with a different set of credentials than site1.

Here is what I tried first, but squid complains of Bungled configuration.

# misc
http_port 3128
auth_param basic program /usr/lib/squid3/basic_ncsa_auth /etc/squid3/passwd
auth_param basic realm proxy

# Site 1 can only be accessed by user_site1
acl site1 proxy_auth user_site1
acl site1 src 192.168.100.21
acl site1 dst site1
http_access allow site1

# Site 2 can only be accessed by user_site2
acl site2 proxy_auth user_site2
acl site1 src 192.168.100.22
acl site2 dst site2
http_access allow google_auth site2

# All other sites will be denied 
http_access deny all

Is it possible to configure squid to somehow group proxy_auth to a particular acl name? How to restrict certain user ids to certain destination sites?

Thank you for all the help