Create Authentication wiki page

[jvt]

Take all authentication-related documentation and consolidate it on a single page in the wiki. In here should be documentation for all /api/session routes, including query parameters, body parameters, headers required, and expected responses.

[alkenerly]

Hey I think when I originally created this doc, I was confused on sending the plaintext pwd. The doc might be wrong is what I'm saying. Might wanna double check that stuff