Multi-tenancy: как изолировать данные клиентов в SaaS на .NET?

public interface ITenantContext { Guid TenantId { get; } }

public sealed class TenantContext : ITenantContext
{
    private Guid? _id;
    public Guid TenantId => _id ?? throw new InvalidOperationException("Тенант не определён");
    public void Set(Guid id) => _id = id;
}

app.Use(async (ctx, next) =>
{
    var claim = ctx.User.FindFirst("tenant_id")?.Value;           // источник истины — подписанный токен
    if (claim is null || !Guid.TryParse(claim, out var tenantId)) { ctx.Response.StatusCode = 403; return; }
    ctx.RequestServices.GetRequiredService<TenantContext>().Set(tenantId);
    await next();
});

public interface ITenantOwned { Guid TenantId { get; set; } }

public class ShopDbContext(DbContextOptions<ShopDbContext> o, ITenantContext tenant) : DbContext(o)
{
    public DbSet<Order> Orders => Set<Order>();

    protected override void OnModelCreating(ModelBuilder b)
    {
        foreach (var et in b.Model.GetEntityTypes().Where(t => typeof(ITenantOwned).IsAssignableFrom(t.ClrType)))
        {
            // e => e.TenantId == tenant.TenantId — значение берётся из текущего экземпляра контекста на каждый запрос
            var p = Expression.Parameter(et.ClrType, "e");
            var body = Expression.Equal(
                Expression.Property(p, nameof(ITenantOwned.TenantId)),
                Expression.Property(Expression.Constant(this), nameof(CurrentTenantId)));
            b.Entity(et.ClrType).HasQueryFilter(Expression.Lambda(body, p));
            b.Entity(et.ClrType).HasIndex(nameof(ITenantOwned.TenantId));
        }
    }

    private Guid CurrentTenantId => tenant.TenantId;

    public override Task<int> SaveChangesAsync(CancellationToken ct = default)
    {
        foreach (var e in ChangeTracker.Entries<ITenantOwned>())
        {
            if (e.State == EntityState.Added) e.Entity.TenantId = tenant.TenantId;
            else if (e.Property(x => x.TenantId).IsModified)
                throw new InvalidOperationException("Нельзя менять тенанта у существующей записи");
        }
        return base.SaveChangesAsync(ct);
    }
}

ALTER TABLE orders ENABLE ROW LEVEL SECURITY;
ALTER TABLE orders FORCE ROW LEVEL SECURITY;

CREATE POLICY tenant_isolation ON orders
    USING (tenant_id = current_setting('app.tenant_id')::uuid)
    WITH CHECK (tenant_id = current_setting('app.tenant_id')::uuid);

public sealed class TenantConnectionInterceptor(ITenantContext tenant) : DbConnectionInterceptor
{
    public override async Task ConnectionOpenedAsync(DbConnection conn, ConnectionEndEventData data, CancellationToken ct = default)
    {
        await using var cmd = conn.CreateCommand();
        cmd.CommandText = "SELECT set_config('app.tenant_id', @t, false)";
        var p = cmd.CreateParameter(); p.ParameterName = "t"; p.Value = tenant.TenantId.ToString(); cmd.Parameters.Add(p);
        await cmd.ExecuteNonQueryAsync(ct);
    }
}