Compiler Error: BC30451: 'DefaultAuthenticationTypes' is not declared. It may be inaccessible due to its protection level.

Hello
I am getting the above error on my aspx page. Specifically, the error states:
Source Error:
Line 10: ' This is required if your application allows users to login Line 11: app.UseCookieAuthentication(New CookieAuthenticationOptions() With { Line 12: .AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie, Line 13: .LoginPath = New PathString("/Account/Login" ...