Unauthorized client.

[Aha Radio]

Hi, 

 We are using rdio to get music from rdio in our app. We have used OAuth2.0 for authentication. Currently we are using authorization code which is documented in (http://www.rdio.com/developers/docs/web-service/oauth2/auth-code/ref-oauth2-auth-code) . 

I am exploring to switch to Resource owner credentials documented in (http://www.rdio.com/developers/docs/web-service/oauth2/auth-password/ref-oauth2-auth-password ).  

I have created the app in rdio site, obtained the client_id and client_secret. I am making POST call to https://services.rdio.com/oauth2/token and passing username=<client_id> password=<client_secret> (HTTP Authorization header method of client verification) . The response comes as "error_code":"unauthorized_client"

"error_description": "This client is not authorized to use the password grant". I have tried to substitute username and password with real username and password, but that doesn't work. Is it the validity of client_id and client_secret that is the issue? 

I've followed all the steps to T. Please let me know what am i doing wrong? 

Regards

Vinay