SPIKE: WCAG 2.0 compliance re: length of login session in the LMS app

[WCAG 2.0 Success Criterion 2.2.1 Timing Adjustable](https://www.w3.org/TR/WCAG21/#timing-adjustable) stipulates that users must be able to turn off, adjust, or extend time limits unless that time limit is greater than 20 hours.

To make sure we're fully compliant here, we need to:
- [ ] Determine how long an authentication session lasts in the LMS context
- [ ] If a login session is less than 20 hours, propose and implement a solution that brings us to compliance

@robertknight mentioned that a likely solution would be to just silently refresh the auth token for users in the background up to 20 hours (that way we don't have to design and implement UI elements to provide the option of extending a login session)