How to use Auth0 service in unity app?

Is there any plugin or any class library so that i can integrated in my app .

I’m afraid that there is no SDK specific to the Unity engine. There is a .NET SDK]1 that can streamline some of calls to Auth0 HTTP endpoints available in the Authentication API, however, depending on which type of authentication you’re going to use in your application then you may need something in addition to that library. For example, social authentication would requiring doing what is described at: Call Your API Using the Authorization Code Flow with PKCE