We have a Lync 2013 installation and are currently in the process of testing SIP functionality. Our current SIP trunk requires a username and password to authenticate. I can't find an awful lot of documentation for Lync on this.
Is there a way of configuring credentials for a SIP trunk in Lync, or is this just not do-able?
I can't help with Lync username/password authentication I'm afraid. If you're in the UK, I can recommend a ST provider who use the IP address, NOT a sign-on, to validate your connection. This is confirmed to work with Lync.