Add Logout button

[T4rk1n]

Add a logout button, performs a form post request to a logout_url.

Prop	Type	Default	description
id	string	-	Id of the button.
label	string	logout	Text of the button
logout_url	string	-	Url to submit a post logout request.
style	object	-	style of the button.
className	string	-	CSS class for the button.

[T4rk1n]

https://github.com/plotly/streambed/issues/11817

[scjody]

Would it make sense to automatically set the default logout_url if DASH_LOGOUT_URL exists in the environment as discussed at https://github.com/plotly/streambed/issues/11817#issuecomment-438801947?

I leave it up to the dash team to decide if this is worth doing, but without this all Dash Apps wanting to add a logout button on DDS will have to implement this so there's a good argument for centralizing it in dcc.

[T4rk1n]

@scjody

There is no python hooks for the components so we can't do it at the component level. Can add it from a dds app with dcc.LogoutButton(logout_url=os.getenv('DASH_LOGOUT_URL')).

[scjody]

That URL doesn't look so bad, except you'll want a default so it doesn't crash in test environments and for non-DDS users. So something like: dcc.LogoutButton(logout_url=os.getenv('DASH_LOGOUT_URL', 'https://dash.plot.ly/docs_on_logout'))

Is it impossible to check DASH_LOGOUT_URL in this function? (I don't know how LogoutButton.py gets generated so I accept that it may not be, but it seems strange that we wouldn't have control over the backend of all our components.)

[T4rk1n]

The python component class is auto-generated, it will get overwritten when the components are regenerated.

[scjody]

I realize that, but I'm surprised we don't have any control over the generation process or what goes into the component at that time.

Anyway if my suggestion is unreasonable I'm OK leaving things as they are.

[T4rk1n]

W could have some kind of hooks, it's just not implemented right now. I created an issue:

plotly/dash#464

[valentijnnieman]

Here if className is undefined, it will add "undefined" to the class. Would be cleaner to check if className exists before appending it.

[valentijnnieman]

I'm getting 405 errors, saying "The method is not allowed for the requested URL.". Is there something we have to set-up in the underlying Flask server to allow for POST requests? Not sure why I'm getting these errors.

For the default url, how about adding it as a defaultProp? You could even do a GET instead of a POST if there's no url set (and therefore uses the default "https://dash.plot.ly/docs_on_logout") so that it links you to those docs.

Lastly, requesting a small change having to do with appending the className prop.

[T4rk1n]

@valentijnnieman

There's an example in the test:

@app.server.route('/_logout', methods=['POST'])
def on_logout():
      rep = flask.redirect('/logged-out')
      rep.set_cookie('logout-cookie', '', 0)
      return rep

[T4rk1n]

I'll make https://dash.plot.ly/dash-core-components/logout_button the default url and adds documentation and examples there when released.

[valentijnnieman]

@T4rk1n Maybe add some more info (or a link to those docs) in the docstring for the component as well, so that it's more clear for users what this component is for.

[valentijnnieman]

Great - looks good to me!