Execute alias with sudo at session startup
Enabling pf (with the rdr rule) with a command/alias or a shell script/function in your bash/zsh profile like in your question is neither common nor good practice. It is possible though:

To disable a password prompt modify the sudoers file:

Open Terminal and enter sudo visudo to modify the file /etc/sudoers.

Change the part:

## User privilege specification
##
root ALL=(ALL) ALL
%admin  ALL=(ALL) ALL


to

## User privilege specification
##
root ALL=(ALL) ALL
%admin  ALL=(ALL) ALL
your_username ALL=(ALL) NOPASSWD: /sbin/pfctl


and save the file.

If you don't know vi: after entering sudo visudo you have to change to insert mode by hitting i. Enter the additional line as indicated above. To leave insert mode hit esc. Then enter :wq and the Enter key to write the modified file to disk and quit vi.

bash:

Entering kiosk-proxy shouldn't require a password anymore. You can then simply add kiosk-proxy as a separate line in your bash_profile (after the alias kiosk-proxy ...line)

After exiting the shell, pf won't be disabled and the passed rule is still redirecting! To disable pf and the rdr rule while exiting the (bash) shell, create a file with touch ~/.bash_logout and the content sudo pfctl -d. 

zsh:

The same works with ~/.zprofile containing:

alias kiosk-proxy="echo \"rdr pass inet proto tcp from any to any port 80 -&gt; 127.0.0.1 port 8080\" | sudo pfctl -ef -"

kiosk-proxy


and ~/.zlogout containing

sudo pfctl -d




A more recommended way is to simply add the rdr rule in pf.conf and enable pf while booting.