Setting cookies for multiple sub-domains

Question

Is it possible to set a cookie for http://www.example.com from a PHP file located at https://secure.example.com? I have some code that was given to me, that appears to try and fails at this. I was wondering if this is possible at all.

Solution 1

Webpages can only set cookies for the second (or higher) level domain that they belong to.

This means that secure.example.com can read and set cookies for secure.example.com or .example.com, the latter of which can also be read and set by www.example.com

One last note: If the secure flag is set on a cookie, it can only be read and set over an https connection.

Solution 2

If you set the cookie domain to ".example.com", the cookie will work for all subdomains.

Comments

[nilacqua]

I wondering if I could be specific to which domains the cookie is sent to.

[Piskvor left the building]

@nilacqua: No. If the cookie is set for .example.com, it will be visible for any subdomain of example.com

[louis.luo]

Hi @Powerlord, does that mean I can use the Javascript on secure.example.com to set a cookie for .example.com too? By just changing the value for document.cookie? Thx

[Powerlord]

@Louis_PIG I don't have a lot of experience dealing with cookies in JavaScript. I would think you'd be able to do that, though... as I recall, it's part of the Cookie standard.

[louis.luo]

Thanks @Powerlord . I am dealing with some problem like this, but your answer at least confirmed that this should be possible. Thanks!

[Michael]

So if you own a.example and b.example.com but nothing else .example.com then this isn't a viable solution...

[Matt]

Would this work for all subsub domains as well. Like would .example.com work on sub.example.com and sub.sub.example.com? Or would you have to do .sub.example.com to make that work?

[zomars]

This won't work on www-less domains tho https://example.com