In BrainzUtils' CustomFlask we enable the flask debug toolbar if the parameter is set and DEBUG is true: https://github.com/metabrainz/brainzutils-python/blob/18229350b764201e966fb9d89784d4e2258a95c6/brainzutils/flask/__init__.py#L33-L34

However, configuration in MeB projects typically isn't loaded until after the CustomFlask object is created (https://github.com/metabrainz/listenbrainz-server/blob/563e83ee88844f0d47f6af4514a659bfc396284e/listenbrainz/webserver/__init__.py#L43-L47). Debug toolbar also requires a SECRET_KEY to be set in the config, which means that it's important that we load config before loading the debug toolbar.

Setting FLASK_DEBUG=1 when loading a project may result in:

{{ File "/code/webserver/_init_.py", line 13, in create_app_with_configuration}}
{{ use_debug_toolbar=True}}
{{ File "/usr/local/lib/python2.7/site-packages/brainzutils/flask/_init.py", line 34, in __init_}}
{{ DebugToolbarExtension(self)}}
{{ File "/usr/local/lib/python2.7/site-packages/flask_debugtoolbar/_init.py", line 58, in __init_}}
{{ self.init_app(app)}}
{{ File "/usr/local/lib/python2.7/site-packages/flask_debugtoolbar/_init_.py", line 69, in init_app}}
{{ "The Flask-DebugToolbar requires the 'SECRET_KEY' config "}}
RuntimeError: The Flask-DebugToolbar requires the 'SECRET_KEY' config var to be set

To fix this, we should remove the debug toolbar parameter from the CustomFlask constructor and add a separate method to install it that can be called after configuration is loaded.