I have never tried to get a ticket from a linux machine, but since there isn't any other answer given...I will give it a try.
Can you provide some more information about your network architecture?
Do you use a Linux web server and a Windows QlikView server?
How do you run the QlikView web server, as a windows service or using IIS?
For ticketing you can create a local windows user account on the QlikView Server.
Make it a member of the QlikView Administrators group.
Pass the credentials of this user when requesting a ticket from the linux server.
As far as I know there is no option in QVS to allow one IP address to request a ticket.
You can use IP restrictions if QlikView Webserver is running in IIS.
I have done it before... I don't have a code with me but you are getting the concept wrong.
There is a two phase process. First you have to identify yourself in Qlikview saying that you are the userX and that user is part of the Qlikview Admin Group. After that you ask for a ticket for the userY.
Then what is going on is that with the ticket process Qlikview Server will only see if the request code have the NTNAME for a user that is in the Qlikview Admin group. If that is correct we will give a ticket for the NTNAME requested. There is not checking directly about the "linux user" but the user that is in the request code, that is way using this process is the developer that needs to have the responsability of managing the Qlikview Access. To avoid "tricks" with this process only one session is allowed for each user (offcourse) .
Tell me if this help you or you would like further information.
Vlad, I tried to comment on your blog but it was rejected for banned words so I'll comment here. The code you posed has serious security problems. You sent the qlikview administrator username and password to the end user with the xmlHttp.open line. Just view source in the client browser and you'll see the username and password.
As for the OP, you can certainly get a ticket from a linux machine. As others have said you will need to get a ticket by logging in as a QlikView Administrator user. The difficulty is that you will need to authenticate with NTLM (and probably NTLMv2). We use jcifs with java; there may be an apache module that can do the same. The other option is to qlikview server with IIS and change the authetication on GetTicket.aspx to basic but you should only do this if you have SSL enabled.