Hook onto the workflow action API

hook_workflow_action.py

# Overriding Whitelisted Methods (in my_app/hooks.py)
# ------------------------------
override_whitelisted_methods = {
	"frappe.model.workflow.apply_workflow": "my_app.workflows.apply_workflow"
}

# in my_app/workflows.py

import frappe
from frappe.model.workflow import apply_workflow as model_apply_workflow
from six import string_types
import json

@frappe.whitelist(allow_guest=True)
def apply_workflow(doc, action):
	if isinstance(doc, string_types):
		doc = frappe._dict(json.loads(doc))
	print(doc.name, action)  # you can perform other logic here
	return model_apply_workflow(doc, action)