Set private key file for ssh auth
#include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSH_PRIVATE_KEYFILE, char *filename);
Pass a char * pointing to a filename for your private key. If not used, libcurl defaults to $HOME/.ssh/id_dsa if the HOME environment variable is set, and just "id_dsa" in the current directory if HOME is not set.
If the file is password-protected, set the password with CURLOPT_KEYPASSWD(3).
As explained above
SFTP and SCP
Added in 7.16.1
Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.