Initialize configuration.

def init_config(self, app):
        """Initialize configuration."""
        for k in dir(config):
            if k.startswith('OAUTHCLIENT_'):
                app.config.setdefault(k, getattr(config, k))

        @app.before_first_request
        def override_template_configuration():
            """Override template configuration."""
            template_key = app.config.get(
                'OAUTHCLIENT_TEMPLATE_KEY',
                'SECURITY_LOGIN_USER_TEMPLATE'  # default template key
            )
            if template_key is not None:
                template = app.config[template_key]  # keep the old value
                app.config['OAUTHCLIENT_LOGIN_USER_TEMPLATE_PARENT'] = template
                app.config[template_key] = app.config.get(
                    'OAUTHCLIENT_LOGIN_USER_TEMPLATE',
                    'invenio_oauthclient/login_user.html'
                )