I am using the OAuth Connector block and the provider is on HTTPS (with a self signed certificate, but the fact that is self signed i don't think that it really matters).
When i press the button "Connect with ...", i get the following error:
Exception: Peer certificate cannot be authenticated with known CA certificates in DrupalOAuthClient->get() (line 342 of /webroot/drupal7/sites/all/modules/oauth/includes/DrupalOAuthClient.inc).
Now, as far as i 've searched in that code, there is no way to alter the Curl options in order to add a certificate. There are no module hook or some kind of configuration page in admin section.
That could be a feature request as well, but i thought that having OAuth working with an HTTPS provider is kinda too basic, so i felt like adding it as a bug.