Before I tackle that one, I've got a strange bug happening when I toggle to only allow WP login.
If I'm logged out of WP and FL, and log into WP, then the cookie settings mean that when I load FL I'm logged in already. That's all great.
If I'm logged out of WP and FL, and I go to log in via Fl, I get a popup from WP to login. I enter my details and click to login. Nothin happens for about 10 seconds, and then the window loads wp-admin for that user. I assume it should close and refresh the FL page using the active cookie? If I close the wp-admin box left, and refresh FL expecting it to be logged in since WP is logged in, it doesn't work and remains logged out. If I clik the 'login' link again, the window pops up trying to load wordpress.site/flarum_auth and returns a 404.
To fix this issue of being locked out of FL, I can go back to WP, log out, log back in, and then FL is happily logged in using the cookie.
I have been tinkering a lot on my WP server, so I'm not sure if this is something I've done or is reproducible in the plugin. Any thoughts would be appreciated!