I am using reporting services 2010 and get the following prompt when trying to access the reports:
Open your project/Solution in SSRS tool. Select the report properties (Right click on report project and select properties). Update 'Overwrite dataset' and 'Overwrite datasource' as True. Then go to your shared Datasource properties and select 'credentials' section. There you can select 'Use this username and password' option and set appropriate SQL Server credentials. Click ok and no more Prompting for credentials from frond end :)