CURLOPT_SSH_PUBLIC_KEYFILE man page
CURLOPT_SSH_PUBLIC_KEYFILE — set public key file for SSH auth
#include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSH_PUBLIC_KEYFILE, char *filename);
Pass a char * pointing to a filename for your public key. If not used, libcurl defaults to $HOME/.ssh/id_dsa.pub if the HOME environment variable is set, and just "id_dsa.pub" in the current directory if HOME is not set.
If NULL (or an empty string) is passed, libcurl will pass no public key to libssh2, which then tries to compute it from the private key. This is known to work with libssh2 1.4.0+ linked against OpenSSL.
The application does not have to keep the string around after setting this option.
SFTP and SCP
The "" trick was added in 7.26.0
Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.
curl_easy_setopt(3), CURLOPT_SSH_AUTH_TYPES(3), CURLOPT_SSH_HOST_PUBLIC_KEY_MD5(3), CURLOPT_SSH_PRIVATE_KEYFILE(3).