Azure SharePoint联机问题，GetAuthenticationCookie返回；值不能为null。参数名称：cookieHeader"；

我通过API接口验证SharePoint Online用户。在过去的几年里，它一直运转良好。但是从星期一开始我就犯了错误

值不能为null。参数名称：cookieHeader

有一段代码可以在Azure上托管的API中为SharePoint Online生成HTTPClientHandler

HttpClientHandler result = new HttpClientHandler();
try
{

    SecureString securePassword = new SecureString();

    foreach (char c in userPassword) { securePassword.AppendChar(c); }

    SharePointOnlineCredentials credentials = new SharePointOnlineCredentials(userName, securePassword);

    result.Credentials = credentials;

    string authCookieValue = credentials.GetAuthenticationCookie(new Uri(hostWebURL));

    result.CookieContainer.SetCookies(new Uri(hostWebURL), authCookieValue);

}
catch (Exception ex)
{
    throw ex;
}

return result;

在上面的代码行中，我们得到了“authCookieValue”的空值

我还使用下面的命令通过SharePoint Online Management Shell检查了“LegacyAuthProtocolsEnabled”的值，该值已经为真

$TenantSettings = Get-SPOTenant
$TenantSettings.LegacyAuthProtocolsEnabled