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export function SignatureCheck(
onInvalid: (reason: string) => void = console.error,
) {
const algorithm = { name: "HMAC", hash: { name: "SHA-256" } };
const extractable = false;
const encoder = new TextEncoder();
const hexToUInt8Array = (string: string) =>
new Uint8Array(
(string.match(/[\da-fA-F]{2}/g) || []).map((s) => parseInt(s, 16)),
);
const verify = async (input: {
payload: string;
signature: string;
}, ...secrets: string[]): Promise<boolean> => {
const [secret, ...fallbackSecrets] = secrets;
try {
if (!input || !input.payload || !input.signature || !secret) {
throw "received at least one falsy argument";
}
const { payload, signature } = input;
const sigHex = signature.replace(/^sha\d+=/, "");
if (!/^([\da-fA-F]{2})+$/.test(sigHex)) {
throw "signature not matching expected pattern";
}
const keyBytes = encoder.encode(secret);
const key = await crypto.subtle.importKey(
"raw",
keyBytes,
algorithm,
extractable,
["sign", "verify"],
);
const sigBytes = hexToUInt8Array(sigHex);
const dataBytes = encoder.encode(payload);
const equal = await crypto.subtle.verify(
algorithm.name,
key,
sigBytes,
dataBytes,
);
if (!equal) {
throw "crypto.subtle.verify resolved false";
}
return true;
}
catch (error) {
if (fallbackSecrets.length > 0) {
return verify(input, ...fallbackSecrets);
}
onInvalid("[SignatureCheck.verify] " + error);
return false;
}
};
return { verify };
}