Allow to set cookie domain

[GoogleCodeExporter]

What steps will reproduce the problem?
We have setup a Apache HTTPD reverse proxy with google-authenticator 2 factor 
authentication. We use the reverse proxy as a single point of access to several 
web applications under different subdomains. Currently there is no option to 
set the domain for the authentication cookie, it will use the default which is 
the host from the request. This means when the user authenticates with webapp1 
the cookie's domain will be webapp1.example.com. And when the user accesses 
webapp2 he'll need to re-authenticate. To avoid this we'd like to set the 
domain for the cookie to be example.com and this way the browser would send the 
cookie along with all requests to all of the webapps hosted in subdomains.

What is the expected output? What do you see instead?
I expect to have an option that allows to set the domain for the cookie.

What version of the product are you using? On what operating system?
Version: trunk, revision 22. OS: Ubuntu 14.04

Please provide any additional information below.

Original issue reported on code.google.com by andras.k...@gmail.com on 5 Feb 2015 at 7:13

[GoogleCodeExporter]

I have forked the repo into github and did the necessary changes to enable 
setting domain for the cookie: 
https://github.com/akerekes/google-authenticator/tree/GoogleAuthDomain

Here are the links to diff and patch formatted changes:

https://github.com/akerekes/google-authenticator/compare/master...GoogleAuthDoma
in.diff

https://github.com/akerekes/google-authenticator/compare/master...GoogleAuthDoma
in.patch

Original comment by andras.k...@gmail.com on 5 Feb 2015 at 7:27