Just as you must connect the ASP.NET MVC 5 client to Identity Server 3. You integrate with Identity Server at the protocol level, there are no implementation features, so integration with Identity Server 3 can integrate with Identity Server 4.
Check out the repository of Identity Server 3 samples that use the .NET Framework (not Core): https://github.com/IdentityServer/IdentityServer3.Samples/tree/master/source/Clients
There are 5 MVC 5 clients in this repository.
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