清除固定url的cookie

 NSArray *cookies = [[NSHTTPCookieStoragesharedHTTPCookieStorage] cookiesForURL:[NSURLURLWithString:url]];

    for (int i = 0; i < [cookies count]; i++) {

        NSHTTPCookie *cookie = (NSHTTPCookie *)[cookiesobjectAtIndex:i];

        [[NSHTTPCookieStoragesharedHTTPCookieStorage] deleteCookie:cookie];

    }