Rdio uses OAuth 1.0a / RFC 5849 for access control. To access the API developers must sign up for an account and register a key for their application.
To obtain an access token, first request a request a request token from: http://api.rdio.com/oauth/request_token
then, ask the user to authorize it at the login_url returned and request the access token from: http://api.rdio.com/oauth/access_token
