…nel server app to work

… app

With this setting, we will not need to provide `websocket_origin` as in the
sample code below.

```
import panel as pn
srv = pn.panel(
    pn.widgets.FloatInput(name='an input')
).show(port=5007, websocket_origin="pavics.ouranos.ca")
```

Before, it would display `http://127.0.0.1:8787/status`.

Now it would display `https://pavics.ouranos.ca/jupyter/user/lvu/proxy/8787/status`.

Following https://docs.bokeh.org/en/latest/docs/user_guide/jupyter.html#jupyterhub

======

Define a function to help create the URL for the browser to connect to the Bokeh server.

See below for a reference implementation. You’ll have to either modify this code or assign the URL of your JupyterHub installation to the environment variable EXTERNAL_URL. JupyterHub defaults to JUPYTERHUB_SERVICE_PREFIX in this case.

def remote_jupyter_proxy_url(port):
    """
    Callable to configure Bokeh's show method when a proxy must be
    configured.

    If port is None we're asking about the URL
    for the origin header.
    """
    base_url = os.environ['EXTERNAL_URL']
    host = urllib.parse.urlparse(base_url).netloc

    # If port is None we're asking for the URL origin
    # so return the public hostname.
    if port is None:
        return host

    service_url_path = os.environ['JUPYTERHUB_SERVICE_PREFIX']
    proxy_url_path = 'proxy/%d' % port

    user_url = urllib.parse.urljoin(base_url, service_url_path)
    full_url = urllib.parse.urljoin(user_url, proxy_url_path)
    return full_url

Pass the function you defined in step 2 to the show() function as the notebook_url keyword argument. Bokeh then calls this function when it sets up the server and creates the URL to load a graph:

show(obj, notebook_url=remote_jupyter_proxy_url)

=========

…no need to set it in jupyterhub_config.py anymore

…k behind our JupyterHub