asterisk users - Mar 2005 - SIP secret: argument only for outgoing

Hi,

I am using asterisk as a GW between SIP and the PSTN. So SIP INVITEs are
coming from and sent to my SIP proxy.

The SIP proxy asks for authentication of the INVITE requests. So I have
configured a SIP peer that I use for outgoing:

[outgoing]
type=peer
host=myproxy
username=asterisk
secret=somesecret

The problem is that now for incoming requests, Asterisk matches the
incoming user with that peer (because host == source IP).

I don't want to define a SIP peer for each of my internal users, I'd
like all incoming calls not to match any peer but be treated in the
context=fromsip defined in the [general] section. How can I prevent
incoming calls to be matched to my outgoing peer?

Thanks,
Johan.