在不使用库的情况下用javaScript实现HMAC-SHA256

HMAC-SHA256是一种哈希算法，它需要密钥和消息输入。在JavaScript中，我们可以使用CryptoJS库来实现HMAC-SHA256。但是，如果您不想使用库，可以尝试以下方法：

function hmacSHA256(key, message) {
  const sha256HashLength = 64; // SHA-256 hash length in bytes
  const blockSize = 512; // HMAC block size in bits
  const ipad = 0x36; // Inner padding value
  const opad = 0x5c; // Outer padding value

  // Convert key and message to byte arrays
  const keyBytes = new TextEncoder().encode(key);
  const messageBytes = new TextEncoder().encode(message);

  // If the key is longer than the block size, hash it first
  if (keyBytes.length > blockSize / 8) {
    keyBytes = new Uint8Array(await crypto.subtle.digest('SHA-256', keyBytes));
  }

  // Pad the key with zeros to the block size
  const paddedKey = new Uint8Array(blockSize / 8);
  paddedKey.set(keyBytes);
  paddedKey.forEach((byte, index) => {
    paddedKey[index] ^= ipad;
  });

  // Concatenate the padded key and message
  const concatenated = new Uint8Array(paddedKey.length + messageBytes.length);
  concatenated.set(paddedKey);
  concatenated.set(messageBytes, paddedKey.length);

  // Hash the concatenated value
  const hashed = new Uint8Array(await crypto.subtle.digest('SHA-256', concatenated));

  // Pad the outer key with zeros to the block size
  const outerPaddedKey = new Uint8Array(blockSize / 8);
  outerPaddedKey.set(keyBytes);
  outerPaddedKey.forEach((byte, index) => {
    outerPaddedKey[index] ^= opad;
  });

  // Concatenate the outer padded key and the hashed value
  const finalConcatenated = new Uint8Array(outerPaddedKey.length + sha256HashLength);
  finalConcatenated.set(outerPaddedKey);
  finalConcatenated.set(hashed, outerPaddedKey.length);

  // Compute the final hash
  const finalHash = await crypto.subtle.digest('SHA-256', finalConcatenated);

  // Convert the final hash to a hexadecimal string
  return Array.from(new Uint8Array(finalHash))
    .map((byte) => byte.toString(16).padStart(2, '0'))
    .join('');
}

上面的函数接受密钥和消息字符串作为输入，并返回一个十六进制字符串，它是HMAC-SHA256哈希。请注意，此函数使用JavaScript的Web Cryptography API来执行哈希计算。如果您需要在旧版浏览器上运行此代码，则需要使用polyfill来支持Web Cryptography API。