If you experience anytime SSRS reports prompts for user credentails in Dynamics AX / 365, then the respective datasets in report may use type of AXREPORTDATAPROVIDER / AXQUERY doesn’t parse the users credentails during report run time to DataSource in SSRS DB (ReportServer).
Integrated Windows Authentication(IWA) is the microsoft authentication protocal, using windows login credentials to autheticate the Microsoft product. In Dynamics AX 2009 / 2012 R2 / 2012 R3 uses IWA. If an application is not opening or running close and reopens same way we needs to to SSRS too.
Solution: We needs refresh the credentails flow, so drop the contents in reports folder and recreate and redeploy all the reports