Inspect specified Windows users on specified web applications, to ensure that their SID has the expected value, and update it if desired, in the scope of the content database only (the change is not farm wide)

FixWindowsUsersSid.cs

using Microsoft.SharePoint.Administration;
using Microsoft.SharePoint.Administration.Claims;
using System;
using System.Collections.Generic;
using System.Linq;

namespace InspectUsersId
{
    class UserAccount
    {
        public string Login { get; set; }
        public string ExpectedSID { get; set; }
    }
    internal class Program : IMigrateEntityForWebApplicationCallback
    {
        static bool Whatif = true;
        static string[] WebAppsToProcess = { "http://spsites", "https://anon.contoso.local/" };
        List<UserAccount> UserAccountsToVerify = new List<UserAccount>
        {
            new UserAccount {Login = "contoso\\user1", ExpectedSID = "S-1-5-21-2647467245-1611586658-188888215-9101"},
            new UserAccount {Login = "contoso\\user4", ExpectedSID = "S-1-5-21-2647467245-1611586658-188888215-16101"},
        };
        static void Main(string[] args)
        {
            //WebAppsToProcess = new string[] { "https://anon.contoso.local/" };
            //Whatif = false;

            Program migrator = new Program();
            SPMigrateEntitiesOperationParameters settings = new SPMigrateEntitiesOperationParameters();
            foreach (string url in WebAppsToProcess)
            {
                SPWebApplication webApp = SPWebApplication.Lookup(new Uri(url));
                if (webApp == null || webApp.ContentDatabases.Count == 0) { continue; }
                foreach (SPContentDatabase db in webApp.ContentDatabases)
                {
                    settings.AddDatabaseToMigrate(db);
                }
                Console.WriteLine($"Processing web application '{webApp.Name}'");
                webApp.MigrateEntities(migrator, settings);
            }
            Console.WriteLine("Finished.");
            Console.ReadLine();
        }

        public SPMigrateEntityCallbackResult ConvertEntity(SPClaimMigrationContext context, SPMigrationEntity entity)
        {
            // Prechecks to skip what is needed
            if (entity.NameClaim == null || entity.KeyClaim == null) { return SPMigrateEntityCallbackResult.Skipped; }
            SPOriginalIssuerType loginType = SPOriginalIssuers.GetIssuerType(entity.NameClaim.OriginalIssuer);
            if (loginType != SPOriginalIssuerType.Windows) { return SPMigrateEntityCallbackResult.Skipped; }
            var userAccount = UserAccountsToVerify.First(x => String.Equals(x.Login, entity.NameClaim.Value, StringComparison.CurrentCultureIgnoreCase));
            if (userAccount == null) { return SPMigrateEntityCallbackResult.Skipped; }
            if (String.Equals(entity.KeyClaim.Value, userAccount.ExpectedSID, StringComparison.CurrentCultureIgnoreCase)) { return SPMigrateEntityCallbackResult.Skipped; }

            string newSidValue = userAccount.ExpectedSID;
            SPClaim newKey = new SPClaim(entity.KeyClaim.ClaimType, newSidValue, entity.KeyClaim.ValueType, entity.KeyClaim.OriginalIssuer);
            string newKeyString = SPClaimProviderManager.Local.EncodeClaim(newKey);

            string contentdb = context.Site != null ? context.Site.ContentDatabase.Name : "null";
            if (Whatif)
            {
                Console.WriteLine($"[{contentdb}] Would change the SID of entity '{entity.NameClaim.Value}' from '{entity.KeyClaim.Value}' to '{newKey.Value}'");
                return SPMigrateEntityCallbackResult.Skipped;
            }
            else
            {
                Console.WriteLine($"[{contentdb}] Change the SID of entity '{entity.NameClaim.Value}' from '{entity.KeyClaim.Value}' to '{newKey.Value}'");
                entity.MigratedKey = newKeyString;
                entity.MigratedName = SPClaimProviderManager.Local.EncodeClaim(entity.NameClaim);
                return SPMigrateEntityCallbackResult.Success;
            }
        }

        public bool IntializaForWebApplication(SPWebApplication webApp)
        {
            return true;
        }
    }
}