Allow extracting and logging in with cookie

[bboe]

In addition to providing a password in combination with the username, PRAW should support passing in cookie= to set a session from a known cookie. For full compatibility the cookie should be able to be stored in the config file.

If both a cookie and a password are given, that should mean -- attempt to use the cookie (verify that authentication works), if it does not, then use the provided password.

In the event the cookie does not work and no password is provided, an appropriate exception should be raised.

Finally, there should be a method to fetch the cookie-string from a logged-in Redditor.

[Damgaard]

I disagree with this. Configuration and Authentication are already very complicated areas of PRAW and this will make it even more so. For me the benefit gained by it is too little to justify the increase in complexity. It will only save a single API call and only when initializing PRAW. So the only users who will really benefit are those who are consuming the API at the maximum rate and are often initializing a new PRAW instance. That seems like an extraordinarily rare occurrence.

[bboe]

While I don't think there is that much added complexity involved, I agree there is little benefit. Especially given that reddit appears to want to shift to OAuth. I'll close this for now, and if someone is really interested in it (i.e., willing to implement it), then they can reopen it.