When users of the Jet Web Portal want to access data sources that require user-specific login credentials, they must - at least once - access the data source settings through the Jet Excel add-in.
This applies to any Dynamics GP, Jet Data Warehouse, Universal, Cube (over IIS), Jet Remote Data Service, Dynamics NAV Web Services, or Dynamics NAV SQL Server data source.
Let's look at an example using a Dynamics NAV 2013 or later (SQL Server) connection.
The system administrator has set the Scopes for this data source connection to require that each user provide their own - user-specific - user name and password.
This means that the default for the data source is that the user name and password are undefined.
Before a user on the Jet Web Portal can run a report that reads from that data source, the user must first run Microsoft Excel with the Jet add-in and enter their user name and password in the Data Source Settings:
In some environments, not every user has Excel (nor the Jet Excel add-in) installed on their system. In those situations, there are alternatives to enable accessing the Data Source Settings.
If your environment would allow every Jet user to access the database with the exact same user permissions, you can configure a single user for accessing the data.
The Scope for those settings would then be configured for Shared:
Another option available to you would be to configure a single system with Excel, the Jet add-in, access to the Jet Service Tier, and Remote Desktop Services. Users could then connect to that system (once), set up with user credentials, and then be able to run reports from the Jet Web Portal.