Now when I run this command:
/usr/bin/python ~/google_appengine/appcfg.py update ~/cdn
I should write email and password. And it is keeping some time, but after a day, I should write email and password again.
How can I keep my auntification (email and password) for long time (month, year)?
This is the intended behaviour.
The best you can do is to stash your password in some file, and use the --email and --passin command line options, for example:
appcfg.py update ~/cdn [email protected] --passin < /path/to/my/passwd
Where passwd is a file that contains only your password.
This way you're just one Ctrl-r away from updating your favorite App Engine app.