User sessions

The 4D web server provides built-in features for managing user sessions. Creating and maintaining user sessions allows you to control and improve the user experience on your web application. When user sessions are enabled, web clients can reuse the same server context from one request to another.

Web server user sessions allow to:

• handle multiple requests simultaneously from the same web client through an unlimited number of preemptive processes (web server sessions are scalable),
• share data between the processes of a web client,
• associate privileges to user sessions,
• handle access through a Session object and the Session API.

Note: The current implementation is only the first step of an upcoming comprehensive feature allowing developers to manage hierarchical user permissions through sessions in the whole web application.

Enabling sessions

The session management feature can be enabled and disabled on your 4D web server. There are different ways to enable session management:

• Using the Scalable sessions option on the "Web/Options (I)" page of the Settings (permanent setting):

This option is selected by default in new projects. It can however be disabled by selecting the No sessions option, in which case the web session features are disabled (no Session object is available).

• Using the .scalableSession property of the Web Server object (to pass in the settings parameter of the .start() function). In this case, this setting overrides the option defined in the Settings dialog box for the Web Server object (it is not stored on disk).

The WEB SET OPTION command can also set the session mode for the main Web server.

In any cases, the setting is local to the machine; so it can be different on the 4D Server Web server and the Web servers of remote 4D machines.

Compatibility: A Legacy sessions option is available in projects created with a 4D version prior to 4D v18 R6 (for more information, please refer to the doc.4d.com web site).

Session implementation

When sessions are enabled, automatic mechanisms are implemented, based upon a private cookie set by 4D itself: "4DSID_AppName", where AppName is the name of the application project. This cookie references the current web session for the application.

The cookie name can be get using the .sessionCookieName property.

1. In each web client request, the Web server checks for the presence and the value of the private "4DSID_AppName" cookie.

2. If the cookie has a value, 4D looks for the session that created this cookie among the existing sessions; if this session is found, it is reused for the call.

3. If the client request does not correspond to an already opened session:

• a new session with a private "4DSID_AppName" cookie is created on the web server
• a new Guest Session object is created and is dedicated to the scalable web session.

The current Session object can then be accessed through the Session command in the code of any web processes.

Web processes usually do not end, they are recycled in a pool for efficiency. When a process finishes executing a request, it is put back in the pool and made available for the next request. Since a web process can be reused by any session, process variables must be cleared by your code at the end of its execution (using CLEAR VARIABLE for example). This cleanup is necessary for any process related information, such as a reference to an opened file. This is the reason why it is recommended to use the Session object when you want to keep session related information.

Sharing information

Each Session object provides a .storage property which is a shared object. This property allows you to share information between all processes handled by the session.

Session lifetime

A scalable web session is closed when:

• the web server is stopped,
• the timeout of the session cookie has been reached.

The lifespan of an inactive cookie is 60 minutes by default, which means that the web server will automatically close inactive sessions after 60 minutes.

This timeout can be set using the .idleTimeout property of the Session object (the timeout cannot be less than 60 minutes).

When a scalable web session is closed, if the Session command is called afterwards:

• the Session object does not contain privileges (it is a Guest session)
• the .storage property is empty
• a new session cookie is associated to the session

Privileges

Privileges can be associated to sessions. On the web server, you can provide specific access or features depending on the privileges of the session.

You can assign privileges usign the .setPrivileges() function. In your code, you can check the session's privileges to allow or deny access using the .hasPrivilege() function. By default, new sessions do not have any privilege: they are guest sessions (.isGuest() function returns true).

In the current implementation (v18 R6), only the "WebAdmin" privilege is available.

Example:

If (Session.hasPrivilege("WebAdmin"))
	//Access is granted, do nothing
Else
	//Display an authentication page
End if

Example

In a CRM application, each salesperson manages their own client portfolio. The datastore contains at least two linked dataclasses: Customers and SalesPersons (a salesperson has several customers).

We want a salesperson to authenticate, open a session on the web server, and have the top 3 customers be loaded in the session.

1. We run this URL to open a session:

http://localhost:8044/authenticate.shtml

In a production environment, it it necessary to use a HTTPS connection to avoid any uncrypted information to circulate on the network.

2. The authenticate.shtml page is a form containing userId et password input fields and sending a 4DACTION POST action:

<!DOCTYPE html>
<html>
<body bgcolor="#ffffff">
<FORM ACTION="/4DACTION/authenticate" METHOD=POST>
	UserId: <INPUT TYPE=TEXT NAME=userId VALUE=""><br/>
	Password: <INPUT TYPE=TEXT NAME=password VALUE=""><br/>
<INPUT TYPE=SUBMIT NAME=OK VALUE="Log In">
</FORM>
</body>
</html>

3. The authenticate project method looks for the userID person and validates the password against the hashed value already stored in the SalesPersons table:

var $indexUserId; $indexPassword; $userId : Integer
var $password : Text
var $userTop3; $sales; $info : Object


ARRAY TEXT($anames; 0)
ARRAY TEXT($avalues; 0)

WEB GET VARIABLES($anames; $avalues)

$indexUserId:=Find in array($anames; "userId")
$userId:=Num($avalues{$indexUserId})

$indexPassword:=Find in array($anames; "password")
$password:=$avalues{$indexPassword}

$sales:=ds.SalesPersons.query("userId = :1"; $userId).first()

If ($sales#Null)
    If (Verify password hash($password; $sales.password))
        $info:=New object()
        $info.userName:=$sales.firstname+" "+$sales.lastname
        Session.setPrivileges($info)
        Use (Session.storage)
            If (Session.storage.myTop3=Null)
                $userTop3:=$sales.customers.orderBy("totalPurchase desc").slice(0; 3)
                Session.storage.myTop3:=$userTop3
            End if
        End use
        WEB SEND HTTP REDIRECT("/authenticationOK.shtml")
    Else
        WEB SEND TEXT("This password is wrong")
    End if
Else
    WEB SEND TEXT("This userId is unknown")
End if