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

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

<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 (markup):

It doesn't work, should it?

I Have also tried, something like

<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 (markup):

I'm not getting very far, please help me - I've read some much conradicting rubbish its making me more and more confused!

Thanks!

 

Sorry to bump my own thread, but I'm getting realy confused and can't find any decent documentation. Can someone at least a good book?