Hi all!

I encountered an interesting situation. 

It is related to UA registration and Registrar changing realm on the fly. When
UA registers for the first time, registration is challenged. As part of 407
there is a realm="REALM1". UA uses this realm to calculate MD5 response. Also
it
keeps registering for some time without problems. At one point in time
Registrar may change realm to "REALM2". UA registers, it gets challenged with
407 and "REALM2". However when it calculates MD5 it still uses "REALM1" and not
"REALM2" found in the last 407. See below:
 
UA                           Registrar
------------REGISTER------------->
<-----  407 (realm=REALM1)--------
-------REGISTER with MD5--------->
<-------------200 OK--------------
...
------------REGISTER------------->
<-----  407 (realm=REALM2)--------
-------REGISTER with MD5--------->
<-------------407-------------- //wrong MD5 cause UA used REALM1 and not REALM2

1. Can Registrar have liberty to change realm in 407 between REGISTER requests?
2. How should UA react if it gets different realms for 2 different REGISTERs?
Some UA cached REALM1 and used it all the time not respecting that Registrar
required REALM2 to be used.

My take would be that Registrar can change realm for different REGISTER
requests. Also, I expect UAs to use all parameters found in the last 407
received and not to cache anything.

Regards,
Zarko Coklin

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