Could you please tell us, does this behavior occurred every time you tried to login, or it happend only once? Would it be possible for you to delete your browser cache and inform us if the problem still persist? It will be good for us to know if you are getting some errors in the Console or .NET tabs when you are not able to login. Any additional information will be much appreciate.
Basically, calling SecurityManger for authentication is the proper way to authenticate a user as it automatically creates authentication cookie which is persisted after the redirect:
var result = SecurityManager.AuthenticateUser(
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