Security Validation and Making Posts to Update Data

Applies to: SharePoint Foundation 2010

For reasons of security, by default, Microsoft SharePoint Foundation does not allow you to make posts from a Web application to modify the contents of the database unless you include security validation on the page making the request.

You can update data for a single site or for a site collection by adding a page directive and a FormDigest control to the page that makes the request. The following directive registers the Microsoft.SharePoint.WebControls namespace:

<%@ Register 
   Tagprefix="SharePoint" 
   Namespace="Microsoft.SharePoint.WebControls" 
   Assembly="Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>

Include a FormDigest control within the form, as follows:

<form id="Form1" method="post" runat="server">
   <SharePoint:FormDigest ID="MyFormDigest" runat="server"/>
   <asp:Button id="Button1" style="Z-INDEX: 101; LEFT: 282px; 
      POSITION: absolute; TOP: 282px" runat="server" 
      Text="Button"></asp:Button>
</form>

Inserting this control on an ASPX page generates a security validation, or message digest, to help prevent an attack wherein a user is tricked into posting data to the server. The security validation is specific to a user, site, and time period and expires after a configurable amount of time. When the user requests a page, the server returns the page with security validation inserted. When the user then submits the form, the server verifies that the security validation has not changed. For more information about this control, see the FormDigest class.

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