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CURLOPT_LOGIN_OPTIONS - set login options #include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_LOGIN_OPTIONS, char *options); Pass a char * as parameter, which should be pointing to the null-terminated options string to use for the transfer. For more information about the login options please see RFC2384, RFC5092 and IETF draft draft-earhart-url-smtp-00.txt CURLOPT_LOGIN_OPTIONS(3) can be used to set protocol specific login options, such as the preferred authentication mechanism via "AUTH=NTLM" or "AUTH=*", and should be used in conjunction with the CURLOPT_USERNAME(3) option. The application does not have to keep the string around after setting this option. NULL Only IMAP, POP3 and SMTP support login options.

CURL *curl = curl_easy_init();
if(curl) {
 curl_easy_setopt(curl, CURLOPT_URL, "smtp://example.com/");
 curl_easy_setopt(curl, CURLOPT_LOGIN_OPTIONS, "AUTH=*");
 ret = curl_easy_perform(curl);
 curl_easy_cleanup(curl);
}

Added in 7.34.0 Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space. CURLOPT_USERNAME "(3), " CURLOPT_PASSWORD "(3), "