Hey @marcuslate,
Here’s one way of doing it:
It uses the free Instant Text plugin as this gives immediate feedback to the user, rather than waiting for the delay in a standard input.
As much as I hate storing data in multiple places, I think that is really the easiest here, so this solution relies on storing the username in two fields, one for the original display and another that should always be lowercase. If you really don’t want to store two values, you could do the lowercase comparison in an advanced :filter operation, but that requires all of your usernames being downloaded to the client in the search, which could be problematic. As you note, you can’t do lowercase (or uppercase) comparison using a search constraint, but you can do it in an advanced :filtered operation. If you want to go that route, this post should help.
Here’s a link to the editor if you are interested in how it works:
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