---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_HTTPSIG_ALGORITHM
Section: 3
Source: libcurl
See-also:
  - CURLOPT_HTTPSIG_HEADERS (3)
  - CURLOPT_HTTPSIG_KEY (3)
  - CURLOPT_HTTPSIG_KEYID (3)
  - CURLOPT_HTTPAUTH (3)
Protocol:
  - HTTP
Added-in: 8.22.0
---

# NAME

CURLOPT_HTTPSIG_ALGORITHM - RFC 9421 HTTP Message Signatures algorithm

# SYNOPSIS

~~~c
#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%

# EXAMPLE

~~~c
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%

# 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).
