.\" generated by cd2nroff 0.1 from CURLOPT_HTTPSIG_ALGORITHM.md
.TH CURLOPT_HTTPSIG_ALGORITHM 3 "2026-09-26" libcurl
.SH NAME
CURLOPT_HTTPSIG_ALGORITHM \- RFC 9421 HTTP Message Signatures algorithm
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTPSIG_ALGORITHM,
                          long algorithm);
.fi
.SH DESCRIPTION
This feature is \fBexperimental\fP 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.
.IP "CURLHTTPSIG_NONE (0)"
Disable HTTP Message Signatures.
.IP "CURLHTTPSIG_ED25519 (1)"
Sign with Ed25519 (RFC 8032). Requires a TLS backend with Ed25519 support.
.IP "CURLHTTPSIG_HMAC_SHA256 (2)"
Sign with HMAC\-SHA256.
.PP
Setting this option to a non\-zero value also sets \fICURLOPT_HTTPAUTH(3)\fP to
CURLAUTH_HTTPSIG. The options \fICURLOPT_HTTPSIG_KEY(3)\fP and
\fICURLOPT_HTTPSIG_KEYID(3)\fP must also be set.
.SH DEFAULT
CURLHTTPSIG_NONE (0)
.SH PROTOCOLS
This functionality affects http only
.SH EXAMPLE
.nf
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);
  }
}
.fi
.SH AVAILABILITY
Added in curl 8.22.0
.SH RETURN VALUE
\fIcurl_easy_setopt(3)\fP returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non\-zero means an error occurred, see
\fIlibcurl\-errors(3)\fP.
.SH SEE ALSO
.BR CURLOPT_HTTPAUTH (3),
.BR CURLOPT_HTTPSIG_HEADERS (3),
.BR CURLOPT_HTTPSIG_KEY (3),
.BR CURLOPT_HTTPSIG_KEYID (3)