Second time I have seen FusionAuth mentioned, so I figured I'd take a look.
Can you provide a link to the source? I can't seem to find it on their GitHub. They only appear to provide install scripts that grab the compiled java application off Google Storage.
Also, you can self-host, but you must agree to a somewhat restrictive license[1] upon install. As I read it, you can only self-host on equipment you own or operate (I don't own or operate EC2), can't deploy for anyone else (no use in consulting), are agreeing to random audits with 30-day notice, and can only use for "Licensee's internal business purposes" (so only auth for internal applications, not public-facing?). Even if these things aren't true, I don't feel comfortable that I understand what I can actually use this for with their current license.