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Impersonation in SharePoint 2010

Posted By:Jean Paul       Posted Date: April 30, 2013    Points: 200    Category: SharePoint    URL: http://www.dotnetspark.com  

In this article we can explore the methods of Impersonation inside SharePoint 2010.
 


In this article we can explore the methods of Impersonation inside SharePoint 2010.

What is Impersonation?


Impersonation is the security feature that enables to control the Identity under which code is executed.  Impersonation gives the following advantages:

·  Run a high privilege code through a low privilege user
·  Record changes in account of another user



What are the Impersonation methods in SharePoint 2010?


SharePoint 2010 provides the following methods of Impersonation:

1.  RunWithElevatedPrivileges to impersonate as System Account user
2.  Passing User Token inside SPSite to impersonate as particular user
3.  Using Windows API

Note: System Account (SHAREPOINT\system) is the application pool user of SharePoint.  If you are using Developer Installations on client operating systems (Windows 7 / Vista) the account name will be different.

Now let us see how to use the above methods.

1.  RunWithElevatedPrivileges

This is the most commonly used method to impersonate.
SPSecurity.RunWithElevatedPrivileges(() =>
  {
  // Your code here
  });

Note: In the case of RunWithElevatedPrivileges the System Account is used to perform the activity.


2.  Passing User Token


SPUserToken is the server model which we use for the purpose.  Each user's token can be represented by this class.  The User Token is actually a byte array. 

The SPUser class contains the property named UserToken.  Passing SPUserToken instance into the SPSite constructor impersonates the particular user.

Eg: new SPSite(UrlText.Text, user.UserToken);

For enumerating all the users of a site the web.Users property can be used.
Eg: web.Users


Running the Code


The attached source contains the following samples:

1.  Enumerate Users


For enumerating users for given website the following code can be used:

using (SPSite site = new SPSite(UrlText.Text))
{
    using (SPWeb web = site.OpenWeb())
    {
        SPContext context = SPContext.GetContext(web);
        var users = context.Web.Users;

        // Display to grid
        usersGrid.DataSource = users.Cast<SPUser>().ToList<SPUser>();
    }
}


On clicking the button we can see the following users as shown below:
-  Please note that there are only 2 users for the site I use
-  The current user logged in is Admin




2.  Create Data Impersonating each User


Now we can try creating list items impersonating each user.  The created item will be having the system property > Created By set to different users:
Following code performs the same:

int count = 1;
foreach (SPUser user in web.Users)
{
    SPSite newSite = new SPSite(UrlText.Text, user.UserToken); // Impersonate
    SPWeb newWeb = newSite.OpenWeb();
    SPListItem item = newWeb.Lists[ListName].AddItem();
    item["Title"] = "Item " + count++.ToString();
    item.Update();

    newSite.Dispose();
    newWeb.Dispose();
}


On running the code above we can see the items created as shown below:
-  Please note that the Created By property is different for each row


Note: An exception will be thrown if any of the user above do not have write permission.

3.  Create Data using RunWithElevatedPrivileges


Now we can try creating the list items using RunWithElevatedPrivileges block.  In this case the user is impersonated to System Account.
The code for the same is shown below:

SPSecurity.RunWithElevatedPrivileges(() =>
    {
        using (SPSite site = new SPSite(UrlText.Text))
        {
            using (SPWeb web = site.OpenWeb())
            {
                SPListItem item = web.Lists[ListName].AddItem();
                item["Title"] = "Item created with RunWithElevatedPriveleges";
                item.Update(); // Item will be created with System Account

                ShowData(web);
            }
        }
    });


We can see that the new item is created with System Account as shown below:


References

Summary


In this article we have explored 2 methods of Impersonation in SharePoint 2010.  The associated code contains the example we have discussed.

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Further Readings:

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