curl / libcurl / API / curl_easy_setopt / CURLOPT_HTTPSIG_KEY

CURLOPT_HTTPSIG_KEY explained

Name

CURLOPT_HTTPSIG_KEY - hex-encoded key for HTTP Message Signatures

Synopsis

#include <curl/curl.h>
 
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTPSIG_KEY, char *key);

Description

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

Pass a null-terminated string containing the hex-encoded private key or shared secret used for RFC 9421 HTTP Message Signatures.

For ed25519, this is the 32-byte private seed (64 hex characters). For hmac-sha256, this is the shared secret as hex; the decoded length is half the number of hex digits, up to CURL_MAX_INPUT_LENGTH / 2 bytes (the same upper bound as other libcurl string options).

PEM and other encodings are not supported; pass the raw key material as hex.

Generating Ed25519 keys

With OpenSSL 3:

openssl genpkey -algorithm ED25519 -out ed25519.pem
openssl pkey -in ed25519.pem -outform RAW | xxd -p -c 64 | tr -d 'n' > key.hex

The key.hex file is one line of 64 hexadecimal digits.

The application does not have to keep the string around after setting this option.

Using this option multiple times makes the last set string override the previous ones. Set it to NULL to disable its use again.

Default

NULL

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 returns a CURLcode indicating success or error.

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