Currently, there are no Wikifunctions/WikiLambda-related grants defined, so sessions authenticated via a bot password or OAuth can’t perform actions like evaluating functions (even when the action is available for anonymous sessions).

I assume this fits somewhere into the hierarchy of T349054: Adjust and improve Wikifunctions user rights grants for General Availability, but I don’t think any part of that task covers this one at the moment (it talks a lot about rights, whereas grants are collections of rights).