town/external/cmd/welcome/README.md

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# welcome command
this command is used to exchange a town invite token for a user account. it is
responsible for:
1. accepting and validating an invite token generated by the `review` command
2. accepting and validating a new user's username choice (ie enforcing rules and checking for dupes)
3. accepting and validating a user's email for use in account recovery (defaulting to an email embedded in the invite token)
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4. accepting and validating a display name (PUT OFF)
5. Confirming that a user agrees to our CoC
6. accepting and validating a user's public ssh key
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upon receipt of these things a user account is created. if it fails, the user
is told about the failure and told to email root@tilde.town for guidance; us
admins get a local mail about the problem.
upon successful creation, `welcome` prints a message on STDOUT suggesting how to log in then quits.
It is risky to let `welcome` create users but no riskier at a high level than the Django admin we had. I can re-use the sudoers trick I did there for the `welcome` user.
## an invite token
an invite token consists of two pieces that are then base64 encoded. the first piece is a random string of 30 characters (alphanumeric and symbols except space) and the second is an email address the invite was sent to; they are separated by a space.
## sudoers config
something like:
```
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welcome ALL=(ALL)NOPASSWD:/usr/sbin/adduser,/usr/sbin/usermod,/town/bin/createkeyfile,/town/bin/generate_welcome_present.sh,/town/bin/registeruser
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```
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I'd like to consolidate adduser/usermod calls into a single "createuser" helper. I'd also like to move the welcome present generation into `welcome`. TODO.
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## user creation flow
once we accept what we need from the user accepting an invite, the flow looks like:
1. create user account
a. run `adduser`, set shell and displayname
b. add user to town group
2. write authorized keys
a. create `~/.ssh`
b. write `~/.ssh/authorized_keys2` and put their key in there
c. write blank `~/.ssh/authorized_keys` with note about adding custom keys
3. generate welcome gift
4. alert hooks (more of a future idea; but it would be nice to have a "WELCOME NEW USER!" in the mailing list / IRC / etc)
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## creating keyfiles
A frustrating hurdle is that `welcome`, just like `ttadmin`, has to write a keyfile that is perms 600 for the new user. This is annoying as shit and requires running `sudo` as the new user. In the old python code:
```python
def write_authorized_keys(self):
# Write out authorized_keys file
# Why is this a call out to a python script? There's no secure way with
# sudoers to allow this code to write to a file; if this code was to be
# compromised, the ability to write arbitrary files with sudo is a TKO.
# By putting the ssh key file creation into its own script, we can just
# give sudo access for that one command to this code.
#
# We could put the other stuff from here into that script and then only
# grant sudo for the script, but then we're moving code out of this
# virtual-env contained, maintainable thing into a script. it's my
# preference to have the script be as minimal as possible.
with TemporaryFile(dir="/tmp") as fp:
fp.write(self.generate_authorized_keys().encode('utf-8'))
fp.seek(0)
error = _guarded_run(['sudo',
'--user={}'.format(self.username),
'/town/src/tildetown-admin/scripts/create_keyfile.py',
self.username],
stdin=fp)
if error:
logger.error(error)
```
this warrants porting `create_keyfile.py` to a new Go program that can live at `/town/bin/create_keyfile` or wherever.