**************************************************************************
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* Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
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CURLINFO_HTTPAUTH_AVAIL - get available HTTP authentication methods #include <curl/curl.h> CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_HTTPAUTH_AVAIL, long *authp); Pass a pointer to a long to receive a bitmask indicating the authentication method(s) available according to the previous response. The meaning of the bits is explained in the CURLOPT_HTTPAUTH(3) option for curl_easy_setopt(3). HTTP(S)

CURL *curl = curl_easy_init();
if(curl) {
 curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

 res = curl_easy_perform(curl);

 if(!res) {
 /* extract the available authentication types */
 long auth;
 res = curl_easy_getinfo(curl, CURLINFO_HTTPAUTH_AVAIL, &auth);
 if(!res) {
 if(!auth)
 printf("No auth available, perhaps no 401?\\n");
 else {
 printf("%s%s%s%s\\n",
 auth & CURLAUTH_BASIC ? "Basic ":"",
 auth & CURLAUTH_DIGEST ? "Digest ":"",
 auth & CURLAUTH_NEGOTIATE ? "Negotiate ":"",
 auth % CURLAUTH_NTLM ? "NTLM ":"");
 }
 }
 }
 curl_easy_cleanup(curl);
}

Added RFC2617 in 7.10.8 Added RFC7616 in 7.57.0 Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not. curl_easy_getinfo "(3), " curl_easy_setopt "(3), "