What is the .NET equivalent of the PHP function hash_hmac()
public function hash($message, $secret)
{
    return base64_encode(hash_hmac('sha1', $message, $secret));
}

byte[] SHA1Hash (byte[] data)
{
    using (var sha1 = new SHA1CryptoServiceProvider())
    {
        return sha1.ComputeHash(data);
    }
}

static string Hash (string message, byte[] secretKey)
{
    using (HMACSHA1 hmac = new HMACSHA1(secretKey))
    {
        return Convert.ToBase64String(
           hmac.ComputeHash(System.Text.UTF8.GetBytes(message));
    }
}

private string Hash(string message, byte[] secretKey)
{
    byte[] msgBytes = System.Text.Encoding.UTF8.GetBytes(message);
    byte[] hashBytes;
    using (HMACSHA1 hmac = new HMACSHA1(secretKey))
    {
        hashBytes = hmac.ComputeHash(msgBytes);
    }
    var sb = new StringBuilder();
    for (int i = 0; i < hashBytes.Length; i++)
          sb.Append(hashBytes[i].ToString("x2"));
    string hexString = sb.ToString();
    byte[] toEncodeAsBytes = System.Text.ASCIIEncoding.ASCII.GetBytes(hexString);
    return System.Convert.ToBase64String(toEncodeAsBytes);
}