Creates a {@code Subject} instance for the user represented by the given method arguments.
@param token the {@code AuthenticationToken} submitted for the successful authentication.
@param info the {@code AuthenticationInfo} of a newly authenticated user.
@param existing the existing {@code Subject} instance that initiated the authentication attempt
@return the {@code Subject} instance that represents the context and session data for the newly
authenticated subject.
Creates a {@code Subject} instance for the user represented by the given method arguments.
@param token the {@code AuthenticationToken} submitted for the successful authentication. @param info the {@code AuthenticationInfo} of a newly authenticated user. @param existing the existing {@code Subject} instance that initiated the authentication attempt @return the {@code Subject} instance that represents the context and session data for the newly authenticated subject.