Configuring Secure Store and Discussing the Double Hop Issue
If you use windows authentication within your SharePoint environment, and you use NTLM rather than Kerberos as the authentication protocol, you will experience the double hop issues when trying to passthru the users credentials to the external datasource if the datasource resides on a different server to IIS. Within this tutorial we learn how you can use Secure Store within the Data Viewer Web Part to passthru authentication and therefore avoid the double hop issue.