====== Digest Authentication ======
===== Ladder diagram =====
<code>
Client                   wrtc_kit           RTCgate           SIP server
   |                       |                   |                   |
 1 |--changeCredentials()->|                   |                   |
 2 |                       |-------Iam-------->|                   |
 3 |                       |                   |------register---->|
 4 |                       |                   |<--unauthorized----|
 5 |                       |<--unauthorised----|                   |
 6 |<---onAuthenticate()---|                   |                   |
 7 |                       |-------Iauth------>|                   |
 8 |                       |                   |---register+auth-->|
 9 |                       |                   |<-----200 OK-------|
10 |                       |<-----welcome------|                   |
11 |<-----onLoggedIn()-----|                   |                   |
12 |                       |<-----sipreg-------|                   |
13 |<-onSIPRegistration()--|                   |                   |
</code>

6: wrtc_kit raises a [[ixnx:wrtc:js:api:wrtc:onauthenticate|wrtc.onAuthenticate()]] event but usually no such event handler is defined by user. Then wrtc_kit calls [[ixnx:wrtc:js:api:line:authenticate|line.authenticate()]] by itself.