Yes it is [read-only][1], you can't authenticate a user in any way.

> Version 1 is read only. Coming up with
> a solid API is hard enough without
> adding writing and authentication to
> the mix. For the initial release, it’s
> a read-only API. We’ll take on the
> much more challenging problem of
> writing (and authentication) in v2.


  [1]: http://blog.stackoverflow.com/2010/05/stack-exchange-api-public-beta-starts/