Login and logout views could optionally post a message to the user

[Mitar]

Login and logout views could optionally (a setting or view argument could be None by default) post a message to the user informing her that she has been logged in or logged out. In this way user could be informed of this (it is important that user understands what is happening in the background) while redirecting to some other page and not just to the page where this is explicitly written. Like adding additional message parameter to views and then do:

if message:
    messages.success(request, message, fail_silently=True)

Messages could be simply (by default) _("You have successfully logged out.") and _("You have successfully logged in.").

This could be solved also with #5612 but maybe it would be useful to have it in views directly.

[Russell Keith-Magee]

Closing wontfix; #5612 is the right approach for this.