What is ASP.NET impersonation ?

When impersonation is enabled, only your application code runs under the context of the impersonated user. Applications are compiled and configuration information is loaded using the identity of the ASP.NET process.
ASP.NET impersonation is disabled by default. If impersonation is enabled for an ASP.NET application, that application runs in the context of the identity whose access token IIS passes to ASP.NET.

You control impersonation using the identity configuration element.
<configuration>

<system.web>

<identity impersonate="true">

</system.web>

</configuration>

or
<identity impersonate="true" password="********" username="testDoamin\Santosh">