[jdev] SASL EXTERNAL for s2s in jabberd14

[Matthias Wimmer]

> - When do you offer SASL EXTERNAL on an incoming connection? I 
> implemented, that the s2s connection manager always checks the peers 
> certificate as soon as a TLS layer is established. Only if the 
> certificate could be validated (not expired, if the incoming stream 
> had a from attribute if this matches the certificate, signed by a 
> trusted CA, ...) I offer the peer to use SASL EXTERNAL. In all other 
> cases I know that SASL EXTERNAL would fail anyway so I do not have to 
> offer it. Better for the peer to try dialback.


I got asked (on Jabber) how I do this verification and how I know which 
domain the server wants to authenticate later on.

If the connecting server sent a from attribute in the stream root, I am 
checking against this. If there was no from attribute (the other server 
does not have to send this attribute), I just check if the certificate 
is not expired and I can validate the certification chain up to a 
trusted root CA certificate.