animating mask in blender-python script

Hi everybody,
I am trying to build a procedural animated mask to be used for transition in video sequence editor (vse). I have figured out how to “draw” the mask, but I can’t find out how to keyframe the position of points of the splines.
Function “keyframe_insert” requires a “data_path” parameter, but I can’t find out a valid value for this parameter for either layers, splines, or points.

In the movie clip editor I can’t find any property for which context menu “copy data path” is active. If I press ‘I’ in movie clip editor, the resuting operation is “bpy.ops.mask.shape_key_insert()”, but I can’t use this in a script because polling the context fails.

I am working both with version 2.79 and 2.80 beta without big differences.

Thanks to everubody