If a site asks one to authenticate with some web service like Twitter, Github, Reddit, Goole, etc, how do you do this programmatically from Elisp, if it is even possible to do so? I have looked in the manual and did a web search but honestly, I am lost on this.

I want to automate something and am downloading content from a website, but in order to be able to download it, one has to “sign-in” via some of those above-mentioned, for the content to be generated and served.