I couldn't find any official documentation specifying what each parameter to a `sla_miss_callback` callable are. This would be a great addition to know how to properly format the messages sent.
airflow/models/dag.py
"""
        Returns a list of dag run execution dates currently running
        :return: List of execution dates
        """
        runs = DagRun.find(dag_id=self.dag_id, state=State.RUNNING)
        active_dates = []
        for run in runs:
            active_dates.append(run.execution_date)
        return active_dates
    @provide_session
    def get_num_active_runs(self, external_trigger=None, session=None):