npm adduser <username> <password> <email>
Create a user named <username> in the npm registry, and save the
credentials to the .npmrc file. Note that this leaves the password
in your .bash_history, and it is currently stored in the clear in
the config file. So, don't use a password you care too much about.
For now, if you somehow break your .npmrc file, and have forgotten your
password, you're boned. Send an email to i@izs.me and I'll delete the
record from the registry so that you can re-add it.
If you break your .npmrc file, but you remember your password, you
can put your user auth back by using the base64 program like so:
npm config set auth $( echo user:pass | base64 )
Install base64 using whichever method you normally use to put programs on your computer. (apt-get, homebrew, macports, yum, or just download the code and build it yourself.)
Or bug me to to remove your account, and then recreate it.