SoundCloud uses OAuth2 for its auth mechanism.
Register a new application at SoundCloud App Registration, set your application name, website and redirect URI.
Fill Client Id and Client Secret values in the settings:
SOCIAL_AUTH_SOUNDCLOUD_KEY = ''
SOCIAL_AUTH_SOUNDCLOUD_SECRET = ''
Also it’s possible to define extra permissions with:
SOCIAL_AUTH_SOUNDCLOUD_SCOPE = [...]
Possible scope values are * or non-expiring according to their /connect documentation.
Check the rest of their doc at SoundCloud Developer Documentation.