Pre-authorized worker login

[JackUrb]

Overview

As part of the "LIGHT-testing as a crowdsourcing task" goal, this PR includes code to deploy to the main LIGHT server where Mephisto can generate an auth key using a worker id and assignment id, and LIGHT can validate that the keys came from us (as we agree on the secret). This then lets us run the game without requiring logins only for users we generate the context for.

Implementation

Creates a PreauthGameHandler, which requires passing a <user_id>/<context_id>/<preauth_token> triple via url-params. We then combine the user_id and context_id and run through a hash salted by the preauth_secret. Comparing this to the provided preauth_token tells us whether we generated the triple (in which case the user can login) or if someone is trying to break in (in which case we 404).

On successful preauth login, we set three cookies: the preauth user id, the context id, and then an auth token for working on the specific context id. Then when the user connects to the socket, we now check if there is any context set, and if so run through the preauth-based socket authentication. This works similarly to the login, however we're only checking the context_id and new token to see if those match.

We also now pass the user_id and context_id down into the AgentNode of an active player, this way it gets properly logged. This will let us filter out episodes by user_id or context_id on the core LIGHT server once the game is live.

Testing

Local tests pass, current failure is caused by a script labeled test_... that isn't a pytest test in the common_sense project.

[klshuster]

why only first 20 chars?

[JackUrb]

URL length concerns. This should be long enough though that people can't just guess access tokens wildly.