Flux for v1 docs is vague about how to supply security creds when authentication is required

[timhallinflux]

URL for relevant page?

https://docs.influxdata.com/flux/v0.50/guides/executing-queries#influxdb-api

Issue:

There isn't any information about supplying the appropriate security credentials when attempting to access the Flux endpoint. This needs to be fleshed out. Chronograf is ok...as the username:password for the connection is re-used for Flux queries in the same way that it is used for InfluxQL...

But the CLI and CURL need to be described, if security is enabled.

[sanderson]

Resolved by #2760. Will rollout out with InfluxDB 1.8 / Flux 0.65