What is a surrogate credential?

A surrogate credential is a credential that is accepted in place of the user supplying a username and password, or going through the authentication challenge. This surrogate can be an IP address or a cookie. The advantages of using a surrogate is that the end users or client browser receives fewer authentication challenges. The disadvange of using IP surrogates is the assumption of one user, one IP address. The disadvantage of using a cookie surrogate is the assumption that the web client is capable of supporting cookies.  Many web clients are capable of supporting cookies, but not all of them do.  If there are application problems when using a cookie surrogate, you may want to try a different surrogate (IP) or removing authentication altogether for that application to see if there is a problem using cookies or not.