Request using ssl / tls for the transfer
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_USE_SSL, long level);
Pass a long using one of the values from below, to make libcurl use your desired level of SSL for the transfer.
These are all protocols that start out plain text and get "upgraded" to SSL using the STARTTLS command.
This is for enabling SSL/TLS when you use FTP, SMTP, POP3, IMAP etc.
Don't attempt to use SSL.
Try using SSL, proceed as normal otherwise.
Require SSL for the control connection or fail with CURLE_USE_SSL_FAILED.
Require SSL for all communication or fail with CURLE_USE_SSL_FAILED.
FTP, SMTP, POP3, IMAP
Added in 7.11.0. This option was known as CURLOPT_FTP_SSL up to 7.16.4, and the constants were known as CURLFTPSSL_*
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.