Updater

Introduce -update Argument (which starts the updater if a new version is available)
Check for Update via ETag
Download Update File to some tmp Folder
validate update File (checksum)
Restart to the update File with -update Flag
copy updated file over original File
restart via updated file and exit process

Only allow logged in users to download the Update.
POST to /updates with the Session and then get a authenticated URL to download the Update if the Version supplied is lower. Enables A/B Testing and also staged rollouts.

Also, if you want to keep the txt File, use http expire header.