Umbraco-CMS/src/Umbraco.Web.BackOffice/Security/BackOfficeSessionIdValidator.cs


using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Authentication.Cookies;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Extensions;
using System;
using System.Collections.Generic;
using System.Security.Claims;
using System.Text;
using System.Threading.Tasks;
using Umbraco.Core;
using Umbraco.Core.BackOffice;
using Umbraco.Core.Configuration;
using Umbraco.Core.Hosting;
using Umbraco.Extensions;

namespace Umbraco.Web.BackOffice.Security
{
    using ICookieManager = Microsoft.AspNetCore.Authentication.Cookies.ICookieManager;

    /// <summary>
    /// Used to validate a cookie against a user's session id
    /// </summary>
    /// <remarks>
    /// <para>
    /// This uses another cookie to track the last checked time which is done for a few reasons:
    /// * We can't use the user's auth ticket to do this because we'd be re-issuing the auth ticket all of the time and it would never expire
    ///     plus the auth ticket size is much larger than this small value
    /// * This will execute quite often (every minute per user) and in some cases there might be several requests that end up re-issuing the cookie so the cookie value should be small
    /// * We want to avoid the user lookup if it's not required so that will only happen when the time diff is great enough in the cookie
    /// </para>
    /// <para>
    /// This is a scoped/request based object.
    /// </para>
    /// </remarks>
    public class BackOfficeSessionIdValidator
    {
        public const string CookieName = "UMB_UCONTEXT_C";
        private readonly ISystemClock _systemClock;
        private readonly IGlobalSettings _globalSettings;
        private readonly IHostingEnvironment _hostingEnvironment;
        private readonly BackOfficeUserManager _userManager;

        public BackOfficeSessionIdValidator(ISystemClock systemClock, IGlobalSettings globalSettings, IHostingEnvironment hostingEnvironment, BackOfficeUserManager userManager)
        {
            _systemClock = systemClock;
            _globalSettings = globalSettings;
            _hostingEnvironment = hostingEnvironment;
            _userManager = userManager;
        }

        public async Task ValidateSessionAsync(TimeSpan validateInterval, CookieValidatePrincipalContext context)
        {
            if (!context.Request.IsBackOfficeRequest(_globalSettings, _hostingEnvironment))
                return;

            var valid = await ValidateSessionAsync(validateInterval, context.HttpContext, context.Options.CookieManager, _systemClock, context.Properties.IssuedUtc, context.Principal.Identity as ClaimsIdentity);

            if (valid == false)
            {
                context.RejectPrincipal();
                await context.HttpContext.SignOutAsync(Constants.Security.BackOfficeAuthenticationType);
            }
        }

        private async Task<bool> ValidateSessionAsync(
            TimeSpan validateInterval,
            HttpContext httpContext,
            ICookieManager cookieManager,
            ISystemClock systemClock,
            DateTimeOffset? authTicketIssueDate,
            ClaimsIdentity currentIdentity)
        {
            if (httpContext == null) throw new ArgumentNullException(nameof(httpContext));
            if (cookieManager == null) throw new ArgumentNullException(nameof(cookieManager));
            if (systemClock == null) throw new ArgumentNullException(nameof(systemClock));

            if (currentIdentity == null)
            {
                return false;
            }

            DateTimeOffset? issuedUtc = null;
            var currentUtc = systemClock.UtcNow;

            //read the last checked time from a custom cookie
            var lastCheckedCookie = cookieManager.GetRequestCookie(httpContext, CookieName);

            if (lastCheckedCookie.IsNullOrWhiteSpace() == false)
            {
                if (DateTimeOffset.TryParse(lastCheckedCookie, out var parsed))
                {
                    issuedUtc = parsed;
                }
            }

            //no cookie, use the issue time of the auth ticket
            if (issuedUtc.HasValue == false)
            {
                issuedUtc = authTicketIssueDate;
            }

            // Only validate if enough time has elapsed
            var validate = issuedUtc.HasValue == false;
            if (issuedUtc.HasValue)
            {
                var timeElapsed = currentUtc.Subtract(issuedUtc.Value);
                validate = timeElapsed > validateInterval;
            }

            if (validate == false)
                return true;

            var userId = currentIdentity.GetUserId();
            var user = await _userManager.FindByIdAsync(userId);
            if (user == null)
                return false;

            var sessionId = currentIdentity.FindFirstValue(Constants.Security.SessionIdClaimType);
            if (await _userManager.ValidateSessionIdAsync(userId, sessionId) == false)
                return false;

            //we will re-issue the cookie last checked cookie
            cookieManager.AppendResponseCookie(
                httpContext,
                CookieName,
                DateTimeOffset.UtcNow.ToString("yyyy-MM-ddTHH:mm:ss.fffffffzzz"),
                new CookieOptions
                {
                    HttpOnly = true,
                    Secure = _globalSettings.UseHttps || httpContext.Request.IsHttps,
                    Path = "/"
                });

            return true;
        }

    }
}