Allow CAS and database authentication to live side-by-side

[orenyk]

I was re-reading the README and felt like the whole "if you try to switch it will break things" aspect of our current authentication setup was a little off-putting. I think we can allow users to store both optional CAS logins as well as optional passwords and only utilize them when necessary. Here's what I have in mind:

• Add a field to the Users table for cas_login - this can be blank or null
• Add a method that copies one parameter into the username field; this will either be email or cas_login. We can therefore have the app copy the appropriate username into the relevant field depending on the presence of the CAS_AUTH variable. I'm not sure when this happens, maybe when you start the Rails server? It would also have to double check and make sure that all users have a CAS username before trying to switch; if you try to use CAS w/o having a login for every user, the app returns an error message.
• In terms of switching to password authentication, we already allow for password resets using e-mail so that would be the simplest way to go

I don't know when this should happen, but making it possible would be really nice.

[mnquintana]

👍 This is a tough call because we have limited person-hours, but this seems like Pre-Export material to me.

[orenyk]

Yea I know, it would be really nice. I'll stick it on the top of our backlog and we'll see if we can get into v5.1.0. Also, depending on how the semester goes we may try for a second sprint as well, so it would definitely go in then.