> Some of the use cases that are important enough to justify the creation of purpose-specific solutions include federated identity, authorizing access to cross-site resources, and fraud mitigation.

Unpopular opinion: There are no privacy-preserving way for "fraud mitigation".

Either you accept fraud as cost to run business, or do away the privacy. Most business owner don't want the fraudulent user to come back, ever. If we value the privacy of user, we need to harm some business.