title: Airflow experimental REST API FORBIDDEN 403 response
body: <p>My system used to call the experimental REST API to trigger DAGs and everything worked fine.<br />
  When I upgraded from version <code>1.10.3</code> to <code>1.10.12</code> I suddenly receive this error:</p>
  <pre><code>requests.exceptions.HTTPError: ('403 Client Error: FORBIDDEN for url: http://airflow.server/api/experimental/dags/my_dag_name/dag_runs',
   ('request_method', 'POST'),
    ('request_url', 'http://airflow.server/api/experimental/dags/my_dag_name/dag_runs'),
     ('request_headers', {'User-Agent': 'python-requests/2.24.0', 'Accept-Encoding': 'gzip, deflate', 'Accept': '*/*', 'connection': 'close', 'Content-Length': '128',
      'Content-Type': 'application/json'}),
      ('request_body', b'{&quot;run_id&quot;: &quot;manual__2020-10-12T08:50:13.288911+00:00__version__69179146&quot;, &quot;execution_date&quot;: &quot;2020-10-12T08:50:13&quot;, &quot;conf&quot;: null}'))
  </code></pre>