New in Frends 4.6+
The parameter editor will by default mask the inputs if any parameters named "Password" or marked with the PasswordPropertyTextAttribute by the Task library developer. However, the data is still stored to the field in plain text, it will just not be shown in Text input mode. Changing to e.g. Expression input mode will show the actual value. This is because you need to use Environment variables to store sensitive data, and you need to be able to write variable references (e.g. #env.my_password) to the parameter fields.
Therefore, in order to pass sensitive information in parameters so it will never be shown in the UI, you need to:
Store the sensitive data in secret Environment variables, as they are never exposed on the UI.
Use the Environment variable reference as the parameter
Make sure the Task parameter has the hidden icon next to the label. This means the value will not be logged.
Note that if the parameter field does not have the hidden icon, the value may get logged if someone turns up the logging level for the process. To make sure the value is not logged, you can turn off all parameter and result logging for the individual Task from the "Advanced settings", by setting the "Skip logging result and parameters" on.