Javadoc
Parse the cookie value. If validation is successful, then the stream
is read in and a Principal representing the cookie value is returned.
Format of the value is:
UserPrincipal-PrincipalType-ExpirationDateUTC-Base64SignatureToken
where:
UserPrincipal - principal of the user
PrincipalType - principal type
ExpirationDateUTC - long representing the expiration Java date in UTC
Base64SignatureToken - The signature token of the 3 fields above in
Base64 format.