Document authentication/SSL support for http, jolokia and other metricbeats

[ppf2]

Metricbeat modules like http and jolokia actually already support authentication in the product today. This means that we have some stale documentation to update :)

• https://www.elastic.co/guide/en/beats/metricbeat/master/metricbeat-metricset-jolokia-jmx.html#_limitations (For Jolokia, it still talks about not having authentication support as a limitation)
• Documentation for both modules do not provide info on how users will pass in authentication information. If this is done via passing in authorization information in the request headers, it will be nice to provide an example
  • https://www.elastic.co/guide/en/beats/metricbeat/master/metricbeat-module-jolokia.html
  • https://www.elastic.co/guide/en/beats/metricbeat/master/metricbeat-module-http.html
• While we are at it, if these modules also support SSL configuration, it will be helpful to document the available configuration settings as well.

[ppf2]

Example configuration for authentication in metricbeat modules.
Authentication info can be provided either directly in the URL, or as separate settings.

metricbeat.modules:
- module: x
  hosts: ['https://me:secret@localhost']
- module: x
  hosts: ['https://localhost']
  username: me
  password: secret

Example configuration for SSL in metricset modules:

metricbeat.modules:
- module: x
  hosts: ['https://me:secret@localhost']
  ssl.certificate_authorities: ["/etc/pki/root/ca.pem"]

[exekias]

As a reference, these are the supported config params (under ssl): https://github.com/elastic/beats/blob/master/libbeat/outputs/tls.go#L30-L44

[exekias]

headers and timeout settings are also available: https://github.com/elastic/beats/blob/master/metricbeat/helper/http.go#L32