digest-md5 SASL challenges ending with a quoted value are parsed incorrectly (with cyrus-sasl disabled)

[yann]

In the case where parse_challenge is at the last token of a challenge and this token has a quoted value, then it needs to rewind one character when cur is positioned at the terminal NULL.

This fixes an issue where libpurple would parse a realm value (for instance) as 'myrealm"' instead of 'myrealm' resulting in chaos and failure of the SASL negotiation.

I've seen this behaviour with Adium from subversion built with the latest tarball of libpurple. Applying this patch cures the problem (for libpurple without cyrus-sasl. It looks like stable binaries are built without, but cyrus-sasl is enabled in 1.4svn)

exemple of challenge:

algorithm=md5-sess,charset=utf-8,cipher="rc4,3des,des,rc4-56,rc4-40",maxbuf=16777215,nonce="e6439a7176aada7255ef04569a664583",qop="auth,auth-conf,auth-int",realm="dev.local"

and bogus response from libpurple:

username="partya",realm="dev.local"",nonce="e6439a7176aada7255ef04569a664583",cnonce="3d19d459123251610177a3ccfe",nc=00000001,qop=auth,digest-uri="xmpp/dev.local"",response=e8061ff7a5342aad60223db62b6f70e7,charset=utf-8

Thanks,

Yann Kerherve

[darkrain42]

This patch depends on the one in #8207; I believe both are correct.

[datallah]

This was committed in revision [8b089c2f6fe2d4dd78d481892094de09dc76c1ec]. Thanks.

[datallah@…]

(In [f91e508404eacd7f37a7fa35f8bb6be7aec3b68d]):
Attribute Yann Kerherve for the XMPP SASL parser changes. Refs #8206, #8207.