I have a custom security domain that has a majority of content authors in it. I feel like, there is a way, so that rather than optionally having to type in
sitecore\user, you can make your custom security domain optional to enter.
So rather than having to type
my-custom-domain\user, you can just type in user (like you can with any user in the Sitecore security domain).
If anyone can remind me, how to configure this, I would really appreciate it. My recollection is that, you can only have one security domain that is optional to enter, so a consequence would be that any Sitecore security domain users would need to enter in
sitecore\user to login, which is fine.