Auth0 vs OAuth2: What are the differences?
Developers describe Auth0 as "Token-based Single Sign On for your Apps and APIs with social, databases and enterprise identities". A set of unified APIs and tools that instantly enables Single Sign On and user management to all your applications. On the other hand, OAuth2 is detailed as "An open standard for access delegation". It is an authorization framework that enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf.
Auth0 and OAuth2 can be primarily classified as "User Management and Authentication" tools.
Binary.com, Chattermill, and White Rabbit Express are some of the popular companies that use Auth0, whereas OAuth2 is used by Ataccama, BookMeBus, and Mubasher.info. Auth0 has a broader approval, being mentioned in 121 company stacks & 55 developers stacks; compared to OAuth2, which is listed in 10 company stacks and 5 developer stacks.
I started our team on Amazon Cognito because I was a Solutions Architect at AWS and found it really easy to follow the tutorials and get a basic app up and running with it.
When our team started working with it, they very quickly became frustrated because of the poor documentation. After 4 days of trying to get all the basic passwordless auth working, our lead engineer made the decision to abandon it and try Auth0... and managed to get everything implemented in 4 hours.
The consensus was that Cognito just isn't mature enough or well-documented, and that the implementation does not cater for real world use cases the way that it should. I believe Amplify has made some of this simpler, but I would still recommend Auth0 as it's been bulletproof for us, and is a sensible price.