use accessor instead of direct access to field. refs #407.

accessing field directly makes debug little hard, because
IDE cannot make 'call hierarchy' correctly. and it is good
habit on OOP programming, I think.
return currentURL instead of redirectURL. refs #407.

we can use curent URL to redirect in normal case, so
just use 'currentURL' instead of 'redirectURL' if
redirectURL is not specified.
Merge pull request #425 from eller86/407-redirect-from-anywhere

redirect after sign in from anywhere