Read up on CURL. You can specify a cookie jar to use, which means you can copy your normal browser cookies into the file CURL is using.
I have regular credentials to access a specific site (built with OpenCMS). Everyday I download (Save AS) a bunch of pages, parse them and extract the data I need. Is there a way to do it via PHP? Maybe using the cookie that's already been set? Or passing credentials in http request? (I tried but seems OpenCMS won't allow that). I've seen something about stream_context_create but I can't figure out how to do it.