Your use for Switch.pm could be done as well with a dispatch table. That is a hash of code references, like so,

my %dispatch = (

    SQUID => sub {
        $web_proxy = $proxy_address;
    },

    EZPROXY => sub {
        if ($proxy_credentials){
            ($user_name, $password) =
             split /\//, $proxy_credentials;
             $prefix = $proxy_address."user=$user_name&pass=$password&
+url=";
       }   
       else {
           $prefix = $proxy_address."url=";
       }
    }
);

$dispatch{$proxy_type}->();
[download]

Your functions should take arguments and return values, rather than modifying global variables, but I didn't know enough about your app to change that.

CountZero++ is right, repaired. Paste confusion.