Authenticating a specific user via the graph api, and posting to their wall

I am trying to figure out if it would be possible to authenticate a specific user, with said users username and password using the graph api, and the posting a message to their wall.

Is this a possibility with the graph api?

Thanx in advance!

You can present users with a webpage (provided by facebook) for entering their credentials. Facebook will then give you back a 'token' which you can pass into the Graph API to do things on that user's behalf. Read more about this at http://developers.facebook.com/docs/authentication/