update
Updates @auth with the information from @msg and @auth_header, possibly un-authenticating it.
As with ctor@Auth.new, this is normally only used by class@Session.
Return
true if @auth is still a valid (but potentially unauthenticated) #SoupAuth. false if something about @auth_params could not be parsed or incorporated into @auth at all.
Parameters
msg
the #SoupMessage @auth is being updated for
authHeader
the WWW-Authenticate/Proxy-Authenticate header