Verify the Masnet signature in C#

// dotnet add package StandardWebhooks --version 1.1.2   (requires the ASP.NET Core shared framework)
using Microsoft.AspNetCore.Http;
using StandardWebhooks;
using StandardWebhooks.Diagnostics;

public static class CSharpStandardWebhooks
{
    /// <summary>
    /// payload is the unparsed request body; Request.Headers carries the webhook-* headers; the library enforces a 5 minute tolerance.
    /// The library only checks the first signature of the header, so each one is verified on its own (during a rotation the header carries two).
    /// </summary>
    public static bool Verify(string secret, string payload, IHeaderDictionary headers)
    {
        var webhook = new StandardWebhook(secret);
        foreach (var signature in headers["webhook-signature"].ToString().Split(' ', System.StringSplitOptions.RemoveEmptyEntries))
        {
            var single = new HeaderDictionary
            {
                ["webhook-id"] = headers["webhook-id"],
                ["webhook-timestamp"] = headers["webhook-timestamp"],
                ["webhook-signature"] = signature,
            };
            try
            {
                webhook.Verify(payload, single);
                return true;
            }
            catch (WebhookVerificationException)
            {
                // try the next signature
            }
        }
        return false;
    }
}

using System;
using System.Collections.Generic;
using System.Security.Cryptography;
using System.Text;

/// <summary>Verifies a Masnet webhook with the base class library only. rawBody is the exact bytes received.</summary>
public static class CSharpManual
{
    public static bool Verify(string secret, IDictionary<string, string> headers, byte[] rawBody, long nowSeconds, long tolerance = 300)
    {
        if (!headers.TryGetValue("webhook-id", out var id) || !headers.TryGetValue("webhook-timestamp", out var timestamp)
            || !headers.TryGetValue("webhook-signature", out var signatures) || !long.TryParse(timestamp, out var sent)) return false;
        if (Math.Abs(nowSeconds - sent) > tolerance) return false;

        var key = Convert.FromBase64String(secret.StartsWith("whsec_") ? secret.Substring(6) : secret);
        using var hmac = new HMACSHA256(key);
        var prefix = Encoding.UTF8.GetBytes($"{id}.{timestamp}.");
        var signed = new byte[prefix.Length + rawBody.Length];
        prefix.CopyTo(signed, 0);
        rawBody.CopyTo(signed, prefix.Length);
        var expected = hmac.ComputeHash(signed);

        // During a rotation the header carries two signatures separated by a space; any match is valid.
        foreach (var part in signatures.Split(' '))
        {
            var pair = part.Split(',', 2);
            if (pair.Length != 2 || pair[0] != "v1") continue;
            try
            {
                if (CryptographicOperations.FixedTimeEquals(Convert.FromBase64String(pair[1]), expected)) return true;
            }
            catch (FormatException) { /* ignore a malformed entry */ }
        }
        return false;
    }
}