CURLOPT_HTTPSIG_ALGORITHM(3)                          Library Functions Manual

NAME
       CURLOPT_HTTPSIG_ALGORITHM - RFC 9421 HTTP Message Signatures algorithm

SYNOPSIS
       #include <curl/curl.h>

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTPSIG_ALGORITHM,
                                 long algorithm);

DESCRIPTION
       This feature is experimental and may change before it is considered
       stable. We advise against using it in production.

       Enable RFC 9421 HTTP Message Signatures on outgoing requests. Pass a
       long set to one of the values below to select the signing algorithm.

       CURLHTTPSIG_NONE (0)
              Disable HTTP Message Signatures.

       CURLHTTPSIG_ED25519 (1)
              Sign with Ed25519 (RFC 8032). Requires a TLS backend with
              Ed25519 support.

       CURLHTTPSIG_HMAC_SHA256 (2)
              Sign with HMAC-SHA256.

       Setting this option to a non-zero value also sets CURLOPT_HTTPAUTH(3)
       to CURLAUTH_HTTPSIG. The options CURLOPT_HTTPSIG_KEY(3) and
       CURLOPT_HTTPSIG_KEYID(3) must also be set.

DEFAULT
       CURLHTTPSIG_NONE (0)

PROTOCOLS
       This functionality affects http only

EXAMPLE
       int main(void)
       {
         CURL *curl = curl_easy_init();

         if(curl) {
           curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/api");
           curl_easy_setopt(curl, CURLOPT_HTTPSIG_ALGORITHM, CURLHTTPSIG_ED25519);
           curl_easy_setopt(curl, CURLOPT_HTTPSIG_KEY,
                            "9f8362f87a484a954e6e740c5b4c0e84"
                            "229139a20aa8ab56ff66586f6a7d29c5");
           curl_easy_setopt(curl, CURLOPT_HTTPSIG_KEYID, "my-key-id");
           curl_easy_perform(curl);
         }
       }

AVAILABILITY
       Added in curl 8.22.0

RETURN VALUE
       curl_easy_setopt(3) returns a CURLcode indicating success or error.

       CURLE_OK (0) means everything was OK, non-zero means an error occurred,
       see libcurl-errors(3).

SEE ALSO
       CURLOPT_HTTPAUTH(3), CURLOPT_HTTPSIG_HEADERS(3),
       CURLOPT_HTTPSIG_KEY(3), CURLOPT_HTTPSIG_KEYID(3)

libcurl                           2026-09-02      CURLOPT_HTTPSIG_ALGORITHM(3)