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* Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
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CURLOPT_FTPSSLAUTH - set order in which to attempt TLS vs SSL when using FTP #include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_FTPSSLAUTH, long order); Pass a long using one of the values from below, to alter how libcurl issues "AUTH TLS" or "AUTH SSL" when FTP over SSL is activated. This is only interesting if CURLOPT_USE_SSL(3) is also set. Possible order values: Allow libcurl to decide. Try "AUTH SSL" first, and only if that fails try "AUTH TLS". Try "AUTH TLS" first, and only if that fails try "AUTH SSL". CURLFTPAUTH_DEFAULT FTP

CURL *curl = curl_easy_init();
if(curl) {
 curl_easy_setopt(curl, CURLOPT_URL, "ftp://example.com/file.txt");
 curl_easy_setopt(curl, CURLOPT_USE_SSL, CURLUSESSL_TRY);
 /* funny server, ask for SSL before TLS */
 curl_easy_setopt(curl, CURLOPT_FTPSSLAUTH, CURLFTPAUTH_SSL);
 ret = curl_easy_perform(curl);
 curl_easy_cleanup(curl);
}

Added in 7.12.2 Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not. CURLOPT_USE_SSL "(3), " CURLOPT_FTP_SSL_CCC "(3), "