Returns the value of the CustomData connection string property if defined; otherwise, BLANK().
This expression has no parameters.
The content of the CustomData property in the connection string.
Blank, if CustomData property was not defined at connection time.
This function is commonly used in implementing expressions for role-based security when an application uses custom authentication.
IMPORTANT: there are reported performance issues if CUSTOMDATA is used in DAX expressions of the model, including RLS filters and measures, in case the connection string does not include CustomData argument. When this happens, simply passing a value to CustomData in the connection string eliminates the performance issue.
Contributors: Alberto Ferrari, Marco Russo, Kenneth Barber
MSDN documentation: https://docs.microsoft.com/en-us/dax/customdata-function-dax