If "curl.cainfo" is not set (or you are using PHP older than 5.3.7, where the option was introduced), libphutil uses the "default.pem" certificate authority bundle when making HTTPS requests with cURL. This bundle is extracted from Mozilla's certificates by cURL:

http://curl.haxx.se/docs/caextract.html

If you want to use a different CA bundle (for example, because you use self-signed certificates), set "curl.cainfo" if you're using PHP 5.3.7 or newer, or create a file (or symlink) in this directory named "custom.pem".

If "custom.pem" is present, that file will be used instead of "default.pem".

If you receive errors using your "custom.pem" file, you can test it directly with curl by running a command like this:

curl -v --cacert path/to/your/custom.pem https://phabricator.example.com/

Replace "path/to/your/custom.pem" with the path to your "custom.pem" file, and replace "https://phabricator.example.com" with the real URL of your Phabricator install.

The initial lines of output from curl should give you information about the SSL handshake and certificate verification, which may be helpful in resolving the issue.