Merge pull request prometheus#301 from someshkoli/expose-newTLSTripper

http_config: Exposes NewTLSRoundTripper method

Merge pull request prometheus#297 from owen-d/json-tags

Adds json struct tags to mirror yaml ones

Make OAuth 2.0 token_url client_id and client_secret mandatory (prome…

…theus#294)

* Made client_id and client_secret mandatory

Signed-off-by: Levi Harrison <[email protected]>

Read oauth2 secret from file (prometheus#293)

* Read oauth2 secret from file

Signed-off-by: Julien Pivotto <[email protected]>