The “Allow Database Logon Prompting” setting in Report Viewer Settings controls whether users may be prompted interactively for database credentials.
The default setting is off and is recommended for most use cases. If the automatic database logon fails, an error will be displayed. This is often preferred when database user accounts are unknown to end users.
If the setting is turned on and the automatic database logon fails, the user will be prompted for a database logon. This may be helpful for troubleshooting. It also allows for cases where individual users have different database accounts and those accounts must be used to retrieve the correct data for a report.