Creating an overridable session for ABP

AbpSessionExtensions.cs

using System;
using Abp.Runtime.Session;

namespace Abp.Temp
{
    public static class AbpSessionExtensions
    {
        public static IDisposable Override(this IAbpSession abpSession, int? tenantId, long? userId)
        {
            var overridableSession = abpSession as OverridableSession;
            if (overridableSession == null)
            {
                throw new ArgumentException("abpSession should be instance of OverridableSession", "abpSession");
            }

            return overridableSession.Override(tenantId, userId);
        }
    }
}

MyModule.cs

//Replace the session service in PreInitialize of your module

Configuration.ReplaceService<IAbpSession, OverridableSession>(DependencyLifeStyle.Singleton);

MyService.cs

using Abp.Dependency;
using Abp.Runtime.Session;

namespace Abp.Temp
{
    //TEST CODE

    public class MyService : ITransientDependency
    {
        public IAbpSession AbpSession { get; set; }

        public MyService()
        {
            AbpSession = NullAbpSession.Instance;
        }

        public void Test1()
        {
            //...
            using (AbpSession.Override(1,2))
            {
                //using IAbpSession will return tenantId = 1, userId = 2 until using statement ends.
            }
            //...
        }
    }
}

OverridableSession.cs

using System;
using System.Threading;
using Abp.Configuration.Startup;
using Abp.Runtime.Session;

namespace Abp.Temp
{
    public class OverridableSession : ClaimsAbpSession
    {
        private AsyncLocal<SessionOverride> OverridedSession { get; set; }

        public OverridableSession(IMultiTenancyConfig multiTenancy)
            : base(multiTenancy)
        {
            OverridedSession = new AsyncLocal<SessionOverride>();
            OverridedSession.Value = null;
        }

        public override long? UserId
        {
            get
            {
                if (OverridedSession.Value != null)
                {
                    return OverridedSession.Value.UserId;
                }

                return base.UserId;
            }
        }

        public override int? TenantId
        {
            get
            {
                if (OverridedSession.Value != null)
                {
                    return OverridedSession.Value.TenantId;
                }

                return base.TenantId;
            }
        }

        public override long? ImpersonatorUserId
        {
            get
            {
                if (OverridedSession.Value != null)
                {
                    return OverridedSession.Value.ImpersonatorUserId;
                }

                return base.ImpersonatorUserId;
            }
        }

        public override int? ImpersonatorTenantId
        {
            get
            {
                if (OverridedSession.Value != null)
                {
                    return OverridedSession.Value.ImpersonatorTenantId;
                }

                return base.ImpersonatorTenantId;
            }
        }

        public IDisposable Override(int? tenantId, long? userId)
        {
            OverridedSession.Value = new SessionOverride(tenantId, userId);
            return new DisposeAction(() =>
            {
                OverridedSession.Value = null;
            });
        }
    }
}

SessionOverride.cs

using Abp.MultiTenancy;
using Abp.Runtime.Session;

namespace Abp.Temp
{
    public class SessionOverride : IAbpSession
    {
        public long? UserId { get; set; }

        public int? TenantId { get; set; }

        public long? ImpersonatorUserId { get; set; }

        public int? ImpersonatorTenantId { get; set; }

        public MultiTenancySides MultiTenancySide
        {
            get
            {
                return !TenantId.HasValue ? MultiTenancySides.Host : MultiTenancySides.Tenant;
            }
        }

        public SessionOverride(int? tenantId, long? userId)
        {
            TenantId = tenantId;
            UserId = userId;
        }
    }
}