You need to configure the sasl_password parameter:
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
I completely agree with the currently accepted answer. Using Read-Host is a great way to add that user-friendly touch, giving users the option to proceed or halt the process.
But if someone's looking ...