HMAC SHA-256 / 384 / 512 in hex and Base64.
Computed with crypto.subtle. The secret never leaves this page and is not stored anywhere.
Signatures update as you type. Web Crypto requires a non-empty key.
Typical uses: webhook signatures (e.g. X-Hub-Signature-256), API request signing, and token integrity checks. Compare signatures with a constant-time comparison on the server.