Adds a simple HTTP Basic Auth handler which can be registered to
endpoints.
This provides a mechanism for extracting user/password from the auth
header; all further authentication logic is left to the user.
Allows users to specify multiple Endpoints, and register Collectables
to each Endpoint. E.g.,
/metrics
and
/metricsHighCardinality
Can both be served by the same MultiExposer, but may expose different
Collectables. This may be useful if, for example, one wants to scrape
groups of metrics with different frequencies.
Each Endpoint must have a unique URI.
Gregor Jasny