DX: Allow devs to alter loading existing accounts

Thanks for your MR. That's a useful feature indeed, but I added some remarks/toughts to the MR.

Thanks for the review, added my remarks as well. I'll update the MR after your input.

I updated the MR based on some of the review remarks.

Responded in MR.

Changed some class names, added an interface for the validator and fixed some code styles issues.

Looks good to me.

Nitpic: In a couple of docblocks you wrote "authantication" instead of "authentication".

Fixed, thanks for mentioning! Will merge asap, but wanted to do some testing first. Unless you tested it already?

I've tested the default functionality: logging in with an already mapped account, and with an account that wasn't mapped in authmap yet, both worked as expected. Logout still works as expected too. I haven't tested writing a custom event listener yet, but since the default implementation is an event listener as well, I don't expect any problems there.

Automatically closed - issue fixed for 2 weeks with no activity.