The engine is unable to invoke Extension methods. Is this correct understanding?

[MithunChopda]

When trying to invoke Extension methods, the engine throws method not found exception. I am assuming because typeof() returns the base type and thus the extensions methods are not visible. Is this correct understanding? Example: User.Identities.First() here method First is not found

[jamescurran]

That is correct. It's only designed to find instance methods.
I believe getting it to recognize an extension method using the instance method syntax would be quite difficult. It'll probably be easier to get it to recognize the method using the static method syntax: Enumerable.First(User.Identities), but even that would be a major change to the code.