Add /auth/token route

[mbklein]

Steps to test:

• Make sure you delete any .aws-sam directories
• Make sure port 3002 is open to your dev machine
• Start the HTTP API locally: make deps serve-https
• Log in by going to https://.dev.rdc.library.northwestern.edu:3002/auth/login?goto=https://.dev.rdc.library.northwestern.edu:3002/auth/whoami
• Go to https://.dev.rdc.library.northwestern.edu:3002/auth/token
• If you're really feeling completist about it, copy the token and submit it to https://.dev.rdc.library.northwestern.edu:3002/auth/whoami in Postman as a Bearer auth token
• Try it with ?ttl=43200 and see if you get a 12-hour token
• Try it with TTL values that don't make sense (strings, negative numbers, Infinity) and make sure you get error
• Try it with a TTL longer than a week (604800 seconds) and make sure you get an error

[kdid]

Works great! 👍