How can I activate ssh-agent confirmation in MacOSX Leopard?

The agent tries to run a helper program to prompt. On OS X this is not in place by default, so you'll need to provide one (at /usr/libexec/ssh-askpass). I'm currently using one similar to this:

#! /bin/sh  

#  
# An SSH_ASKPASS command for MacOS X  
#  
# Based on script by Joseph Mocker, Sun Microsystems


TITLE=${MACOS_ASKPASS_TITLE:-"SSH Agent"}  

DIALOG="display dialog \"$@\" buttons {\"Deny\", \"Allow\"} default button 2"
DIALOG="$DIALOG with title \"$TITLE\" with icon caution"  

result=`osascript -e 'tell application "Terminal"' -e "$DIALOG" -e 'end tell'`  

if [ "$result" = "button returned:Allow" ]; then
    exit 0 
else  
    exit 1  
fi