add username/password authentication.

[beanieboi]

hey!

first of all, thanks for sondcloud2000! 👍
i implemented the feature mentioned in #16 but i'm not sure what to do with it, maybe someone can take this further.

also i'm not sure how to handle the client_secret, do you have any ideas?

this is how it works:
first auth: start the app with --auth option and provide your username and password
once this is done, the access token gets refreshed every time you start the app

any feedback is welcome!
ben

[georgi]

For obvious reasons it is wrong to expose the client secret.

Unfortunately the soundcloud developer documentation is not clear about that.
The oauth spec offers a couple of possible flows here, all more or less inconvenient:
http://tools.ietf.org/html/draft-ietf-oauth-v2-22#section-9

Actually I think the solution is similar to the client-side flow here:
http://developers.soundcloud.com/docs#authentication

Example: https://soundcloud.com/connect?client_id=609ae0b573913db156968e0ec38c1e26&redirect_uri=http%3A%2F%2Fdevelopers.soundcloud.com%2Fcallback.html&response_type=code_and_token&scope=non-expiring&display=popup

Somehow the user has to see the connect screen, which is a login effectively.
The user-agent redirects to the given redirect url, which also contains the code and the token.
Maybe it is possible to call this endpoint directly with username/password and get back the non-expiring token.