说明

{
    tenantId = tenantId,//租户id
    v = 2,//固定值，2
    timestamp = timestamp,//秒级时间戳(10位)
    param = json,//JSON格式的参数
    sign = sign //签名
}

param格式如下：
{
    platformId = 1,//社交平台唯一id
    externalUserId = 'xxxxx',//好友平台原始联系人标识
    accountId = 'xxxx',//员工社交平台原始账号标识
    userId=10//友米账号id
} 

public static string GetMs5Sign(string tenantId, long timestamp, string paramJson, string aesKey, int v = 2)
{
    //按参数key排序
    SortedDictionary<string, string> treeMap = new SortedDictionary<string, string>(new Comparator())
    {
        ["tenantId"] = tenantId,
        ["v"] = v.ToString(),
        ["param_json"] = paramJson,
        ["timestamp"] = timestamp.ToString(),
    };

    //加密
    StringBuilder signbuilder = new StringBuilder();

    signbuilder.Append(aesKey);//前后加上应用密钥
    foreach (string key in treeMap.Keys)
    {
        if (string.IsNullOrEmpty(key) || string.IsNullOrEmpty(treeMap[key]))
            continue;

        signbuilder.Append(key + treeMap[key]);
    }
    signbuilder.Append(aesKey);//前后加上应用密钥

    #region 转md5 小写

    byte[] bytes = MD5.Create().ComputeHash(Encoding.UTF8.GetBytes(signbuilder.ToString()));
    signbuilder.Clear();

    for (int i = 0; i < bytes.Length; i++)
    {
        signbuilder.Append(bytes[i].ToString("x2"));
    }
    return signbuilder.ToString().ToLower();

    #endregion
}

private class Comparator : IComparer<string>
{
    public int Compare(string x, string y)
    {
        return x.ToLower().CompareTo(y.ToLower());
    }
}