Should I be using mod_ifsetenv? Need authentication only for some users.

[lucoxade]

Hello, I'm a bit confused on how I should be using enviromental variables within an Apache config,

Imagine I only wanted to prompt an authentication box for users with Safari, I have tried this in my userdir.conf on Apace 2.0 on Ubuntu
[code]<Directory /home/*/public_html>

BrowserMatchNoCase ^Safari thisauthtype=Basic thisrequire=valid-user thisauthname="Donkey Boots"
AuthType        thisauthtype
AuthName        thisauthname
AuthScriptFile  "/var/www/hiddenrealywell/auth.php"
Require        thisrequire
</Directory>[/code]
It doesn't work, should it?

I Have also tried, something like
[code]
<Directory /home/*/public_html>
SetEnvIf User_Agent ^Safari dothisthing
<IfDefine dothisthing>
AuthType        Basic
AuthName        "Donkey Boots"
AuthScriptFile  "/var/www/hiddenrealywell/auth.php"
Require          valid-user
</IfDefine>
</Directory>[/code]
I'm not getting very far, please help me - I've read some much conradicting rubbish its making me more and more confused!  ???

Thanks!