A method and system for using an Internet client's local authentication mechanism in systems having updated browser code, so as to enable third party authentication according to an authentication scheme specified by a participating server on clients with updated browser code, while not breaking clients with legacy browser code. A redirect response from a server has authentication data added thereto such that updated browser code can detect the data's presence and enable the use of local security mechanisms for authentication purposes with the server-specified authentication scheme, including local credential entry for verification at a third party login server. At the same time, if such a redirect response is received by prior browser code, the added data is ignored while conventional redirection occurs, such that third party authentication may be performed via redirection to a third party's Internet page that provides a form for credential entry.