package auth

import (
	"crypto/hmac"
	"crypto/sha256"
)

// sha256HMAC computes an HMAC-SHA256 tag.
//
// It is a thin wrapper so that the session store and the OIDC state store
// cannot accidentally diverge on how they sign. The stdlib hmac package already
// performs a constant-time internal comparison; the constant-time requirement
// in this codebase is about how *we* compare the resulting tags.
func sha256HMAC(key, body []byte) [32]byte {
	mac := hmac.New(sha256.New, key)
	mac.Write(body)
	var out [32]byte
	copy(out[:], mac.Sum(nil))
	return out
}