Add the following to `/etc/pf.anchors/myname`:
```shell
rdr pass on lo0 inet proto tcp from any to any port 80 -> 127.0.0.1 port 4000
rdr pass on lo0 inet proto tcp from any to any port 443 -> 127.0.0.1 port 4001
```

Add the following to `/etc/pf-myname.conf`:
```shell
rdr-anchor "forwarding"
load anchor "forwarding" from "/etc/pf.anchors/myname"
```

Add the following to `/Library/LaunchDaemons/com.apple.pfctl-myname.plist`:
```xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
     <key>Label</key>
     <string>com.apple.pfctl-myname</string>
     <key>Program</key>
     <string>/sbin/pfctl</string>
     <key>ProgramArguments</key>
     <array>
          <string>pfctl</string>
          <string>-e</string>
          <string>-f</string>
          <string>/etc/pf-myname.conf</string>
     </array>
     <key>RunAtLoad</key>
     <true/>
     <key>KeepAlive</key>
     <false/>
</dict>
</plist>
```

Run the following command to have it start at boot:
```shell
sudo launchctl load -w /Library/LaunchDaemons/com.apple.pfctl-myname.plist
```