Okta is a SaaS offering that does that. Maybe not fraud. What is fraud in this context? Spam? Check. Lost passwords? Check. Let someone else deal with auth? Check.
All of those are either services or software you can host yourself that provide auth and user management, OTPs, 2FA, email recovery, forgotten passwords, single-sign on, and more.
In what way? verification emails don't count. And for many servers where spam and troll accounts is a problem, custom bots and new member screening features deal with this - since they don't want to spend every waking moment staring at the server and banning people who join and immediately cause issues.
Okta recently partnered with a few folks to tackle this. They published a thing [1] in April. Fraudulent registrations and bots are being screened using Shape which was acquired by F5 [2]. I'm not saying this problem has been solved, but it's an area of active concentration. For most folks, the offerings are more than adequate. For the top saas or platforms, you'll probably always have this issue as you're a lucrative target.
All of those are either services or software you can host yourself that provide auth and user management, OTPs, 2FA, email recovery, forgotten passwords, single-sign on, and more.