The SSRS Execution Account is a default Windows credential used by SSRS when running a report to access resources (e.g. file shares for image files) or databases for report datasources that do not require credentials and where Integrated Security is specified.

If an Execution Account is not specified the SSRS service credentials are used – which is not ideal

It seems convenient to me to use the Execution Account as a default baseline credential for accessing most data sources, provided you don’t need the additional cast iron security (and administration overhead) of setting user access permissions at the database level.

Configuration

1. Create a domain credential – e.g. …DataSourceLogin.
2. Specify this account and password in Reporting Services Configuration Manager  –> Exection Account
3. Edit the SSRS Data Source:
   1. Add “Integrated Security=SSPI;” to the connection string.
   2. Select Credentials are not required  option of “Connect Using”.

(SQL Server 2012)