[SSSD] [sssd PR#198][comment] secrets: support https in proxy provider

[pbrezina]

URL: https://github.com/SSSD/sssd/pull/198
Title: #198: secrets: support https in proxy provider

pbrezina commented:
"""
I changed `POST` method from `CURLOPT_POST` to `CURLOPT_CUSTOMREQUEST = "POST"` since it the first option uses different options to pass data and data length to curl. Now it works even on rhel7.
"""

See the full comment at https://github.com/SSSD/sssd/pull/198#issuecomment-290394404