Auth0 is an OpenID Connect compliant OAuth2 provider, so we're able to
re-use the generic OAuth2 provider to implement it. The routes required
by Auth0 have been hardcoded for user convenience.
Also, Auth0 requires users to register a subdomain of auth0.com when
signing up. This must be provided to chronograf through the
`--auth0-domain` parameter (or `AUTH0_DOMAIN` ENV). This is **distinct**
from the `PUBLIC_URL`. For example, for a Chronograf hosted at
`http://www.example.com`, and an Auth0 domain of
`http://oceanic-airlines.auth0.com`, a client-id of `notpennysboat` and a
client-secret of `4-8-15-16-23-42`, the command line options would look
like:
```
chronograf \
--auth0-domain=http://oceanic-airlines.auth0.com \
--auth0-client-id=notpennysboat \
--auth0-secret=4-8-15-16-23-24
--public-url=http://www.example.com
-t `uuidgen`
```
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