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Retain session when calling from a different website

I have two website consider it as website1 and website2.
In website2 there is a login page .When a user click on the login button it will call a HTTPhandler in website1 to authenticate user.On successful authentication user information will be stored in a Session variable from handler.
Then it will redirect to a page page1.aspx in website1.But the previously set session is not available in the page1.aspx .What will be the issue?
I checked the session id in first request(when calling handler in website 1 from webiste 2) and Second request( redirecting to the page1.aspx from the handler) the session id is different.
How can i retain the session data?

You need to store session data in another process shared to both web site.
You can do it intwo different ways:
Configure an SQL server
Configure SessionState service, a Windows service used to share informations.
In both cases you have to change both web.config files to support the new session mode.
I.e. to use SQL:
Prepare a database (from command prompt):
cd \Windows\Microsoft.NET\Framework\v4.0.30319
aspnet_regsql.exe -ssadd -E -S localhost\sqlexpress
Modify web config as following:
<sessionState mode="SQLServer"
sqlConnectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;Initial Catalog=Test" allowCustomSqlDatabase="true"/>
You don't need to change your code.

Correct me if I an wrong, AFAIK different domains cannot share a single session. One way to handle this is to carry the data to the other site through cookie [encrypt the values for security], then copy this cookie value to the session in the other site receiving it and destroy the cookie.
And if the sites are in different servers you need to handle the "sticky session" so that servers share the session.

This situation sounds kind of similar to one I have experienced and worked on before, where one web application acts as the login page while another is the actual app where all your work is done. I can describe what I did in the hope that you find it useful.
Like you I had one web app which had the login page (so in your example this would be website2). When the login form submitted I then redirect to a fake Login.aspx page in website1 - this is where we differ I think as I'm not sure of your specific reason for using a HttpHandler.
In my case the website2 Login.aspx page is actually just the way into the web application; it has no markup, just code-behind which will authenticate the user, perform setup (e.g. set session variables) and then redirect to another page such as Homepage.aspx. This particular scenario has worked for me, so maybe your problem revolves around the use of a HttpHandler though I would not be able to tell you why.

In order to retain the same session date across two different servers running ASP.NET web applications you must configure your session state to be managed out of process. This means the actual session state data variables will be stored outside of worker process and in another process that is able to make the session data available to other machines.
To achieve this you can configure your application to use SQL Server to store session state and make it available to multiple servers in your farm. The TechNet article Configure a SQL Server to Maintain Session State (IIS 7) provides details on hor this is done in IIS 7.
If you are using IIS 6 then the steps to configure are somewhat different and I can provide further details on this if needed.
In order for this to work you do need to ensure that both servers are running applications within the same domain, e.g. myapp.com, otherwise the ASP.Net session cookie will not be passed between the two servers. ASP.Net uses the cookie to lookup the session state stored in SQL Server and will therefore not find any matching session if the cookie is not passed on requests between the two servers.

i think IRequiresSessionState will not help because context is different.
once we had the same problem but that was passing asp session varibles to .net. How ever you can do it here also.
on both website create a page setsession.aspx
now if you are on page say web1/page5.aspx and want to go to web2/page3.aspx
you redirect to web1/setsession.aspx?togo1=web2/page3.aspx
in both setsession.aspx logic in to extract sessiondata and place them in querystring
so the web1/setsession will redirect to web2/setsession.aspx?sess1=value1&sess2=value2&togo=page3.aspx
web2/setsession.aspx will check for togo querystring and if found will extract all querystring name and value will set them in session and will then redirect to togo value.
you need to differentiate togo1 and togo carefully.

Session sharing between websites is going to require hand-coding. You could hack the asp.net framework to get this working, but I feel that this is not a clean way of achieving what you set out.
If user authentication is all you are doing from website, is it possible to use alternative? Single Sign On mechanisms will help you out here.
Something like SAMLSSO could help you in this case.

You have two websites which are hosted on different servers, it means you have two different processes running on separate machines, so sessions will be definitely different. Same session can't be shared across processes because by default asp.net support in-memory session.
Here you would need to think about storing sessions information which can be shared between two processes (i.e. out of process). Ideal way to store sessions information in databases. For this you can consider Stefano Altieri code sample above.

I don't think you really want to share session information between two websites at all. From what I can gather from comments, what you're really trying to do is have a user authenticate in one website (give you a username and password which are validated) and then have that "logged in" state transferred to another website which doesn't handle authentication for itself.
What you are describing is the Delegated Authentication model.
In this model, your application hands-off authentication to other systems which it trusts to provide information about users.
There are two well-known protocols which provide this mechanism:
OpenID
This is intended to facilitate users logging in with their own identity providers (Google, Facebook, Microsoft Account). It's a very good choice if you're running a public-facing website, as most users will already have an account they can log in with.
WS-Federation
This is intended to facilitate users logging in with identity providers which are managed by known trusted parties, such as partner organisations.
From version 4.5, the .NET Framework has built-in support for WS-Federation via the Windows Identity Foundation component (and is also available for earlier versions as a separate download). This automates the task of delegating your authentication to an Identity Provider.
It also provides components for you to write your own Identity Provider, should you want to create your own, but you shouldn't have to; you can find various existing implementations to perform this job for you.
The problem you're trying to solve is a very difficult one, especially trying to make it secure enough to be reliable. The good news is that smarter people than you or I have spent years working out very clever ways of doing this. You should use what they have done and not try to cobble together something out of Session state.
In the long-run it's best to let the smarter men do the hard work for you.

Asp.net MVC4 Storing sensitive user data

I have a Asp.Net MVC4 website which can connect to multiple databases depending on the user's login credentials. In order to get the database access list for the user, I have to perform a few complex joins when they login. To avoid having to do this more than once, I am currently encrypting and storing the database ID in a cookie. I now realize that this may not be a good idea and even strong encryption may be broken. In addition, the encrypted cookie is transferred around on every request increasing traffic. I am now thinking about using the HttpContext.Current.Cache to store the data instead. Can anyone comment on whether this is a good idea. I would also be interested in knowing if there are better options out there. My website is not deployed on a server farm right now but what would be the implications if I were to use a cache and a server farm in future?

Based on your requirements (i.e. keep a hold of sensitive user specific info across a session), the correct place is for this is the SessionState. AFAIK sessions states can be shared across multiple web servers so if you did use a server farm you wouldn't need to change anything.

Session is right container for user sensitive data. Or you can store it in database and get it there by some identifier that is stored in session(it is useful if you store large amount of data).

Shared Application

I am creating an application to be accessed by multiple clients, but
each customer will have a different database, only access the
same application in IIS, I'm using DDD, C # and MvC3 and Entity Framework 4.1 CF. Does anyone have any example or an idea of how best to configure the connection string
specific to each client?

First, you need to identify whether it's a database per client (machine?), user identity authenticating, or some other identifier. For example, if it's per account, then two machines may be able to authenticate as that account and get the same storage.
Once you have that identifier, you'll need a master table somewhere with a map of account to database connection string. You'll probably also want to cache that table in memory to avoid two db roundtrips on every request.
That global configuration information is typically stored in a database. You could go as simple as a file but that would cause problems if you ever wanted to scale out your front end servers, so common storage is best.

Is it possible to share sessions across subdomains which are different applications?

Is it possible to share sessions across subdomains which are different applications without using Sql Server Session mode? I've implemented this concept with help from this link:
What options are there for sharing data across subdomains?
However is it possible without Sql Server mode may be using in proc etc?

You won't be able to do this using InProc, each application will have its own memory space.
You could set up a web service to get around the issue, although I find this solution to be more of a hack.
You could alternatively use a key/value store database or some flavour of NoSQL.
A custom session state provider would be a more elegant solution.
MongoDB ASP.NET Session State Store Provider

load balancer question c# asp.net

The place where I work has 2 servers and a load balancer. The setup is horrible since I have to manually make sure both servers have the same files. I know there are ways to automate this but it has not been implemented, hopefully soon (I have no control over this). I wrote an application that collects a bunch of information from a user, then creates a folder named after the email of the user in one of the servers. The problem is that I can't control in which server the folder gets created in, so let say a user goes in.. fills his stuff and his folder gets created in server 1, user goes away for a while and goes back to the site but this time the load balancer throws the user into server 2, now the user does something that needs to be saved into his folder but since it didn't created in this server an error occurs. What can I do about this? any suggestions?
Thanks

It sounds like you could solve a few issues by implementing a cloud file service for the file writes such as Amazon S3 http://aws.amazon.com/s3/
Disk size management would no longer be a concern
Files are now written and read from S3 so load balancer concerns are solved
Benefits of a semi-edge network with AWS. (not truly edge but in my experience better than most internally hosted solutions)

Don't store your data in the file system, store it in a database.
If you really can't avoid using the file system, you could look at storing the files in a network share both servers have access to. This would be a terrible hack, however.

It sounds like you may be having a session state issue. It sounds odd the way you describe it, but have a look at this article. It's old, but covers the basics. If it doesn't try googling "asp.net session state web farm"
http://ondotnet.com/pub/a/dotnet/2003/03/24/sessionstate.html

Use NAS or SAN to centralize storage. That same network-accessible storage can store the shared configuration that IIS can be setup to use.
Web Deploy v2 just released from Microsoft, I would encourage the powers that be to investigate that, along with Application Request Routing and the greater Web Farm Framework.

This is a normal infrastructure setup. Below are the two commonly used solutions for the situation you are in.
If you have network attached storage available (e.g. Netapps), you can use this storage to centrally store all of your user files that need to be available across all servers in your web farm.
Redesign your application to store all user specific data in a database.