Bug#868686: proper fix proposed and workaround described

[Barak A. Pearlmutter]

The relevant RFC is here: https://www.ietf.org/rfc/rfc3261.txt

>  SIP URIs [have] a similar form to an email address, typically containing a username and a host name.  In this case, it is sip:bob at biloxi.com, where biloxi.com is the domain

So in the URI sip:bob at biloxi.com, the username is "bob".

This report refers to a "username" as the email address used for
creating the account. If the username itself contains an "@"
character, it would have to be escaped, according to the RFC:

> For each component, the set of valid BNF expansions defines exactly which characters may appear unescaped.  All other characters MUST be escaped.

> For example, "@" is not in the set of characters in the user component, so the user "j at s0n" must have at least the @ sign encoded, as in "j%40s0n".

So to answer this question:

> Given that SIP account names can not contain at signs, what do you suggest the program do when such username is entered?

The answer is: escape it as "%40". But in the meantime, this issue can
be worked around by manually giving the username with the @ escaped in
this fashion.