You can add secured ArcGIS Server map services to the ArcGIS Map Web Part via a proxy URL. Web requests are redirected
through the proxy, which is responsible for authenticating with the service endpoint. Once you have configured your proxy pages as shown in the Configure a proxy topic, you can access secured services.
With the Map Web Part in Edit Mode, click Browse to display the Browse panel.
On the Browse panel, clickAccess secured services. The check box to Add Secured Services and the Configure Proxy link appear.
Click the Configure Proxy link, and in the Configure Secured Services dialog box that appears, enter the URL to the desired proxy page and click OK. The proxy entered will be shared by all layers in the application that use secured services.
Ensure you have entered the proxy url correctly as it is not validated by the ArcGIS Map Web Part.
In the Browse panel, check the Add Secured Services check box. All of the layers you add will now use the defined proxy.
To change the proxy, use the Configure Proxy link in the Browse panel.