setting cross-subdomain cookies accessible to a sub-subdomain?

I've set a coo开发者_开发技巧kie with domain of .example.com. It is available for every first-level subdomain on my site, as it should be.

It is not, however, available on nth level subdomains, i.e. sub.subdomain.example.com and too.many.subdomains.subdomain.example.com don't see the cross-subdomain cookie while subdomain.example.com does. Is there any fix for this?

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The client seems not to follow the rules specified in the rfc. IE fails when there's an underscore in the domain name.

See https://www.rfc-editor.org/rfc/rfc6265#section-5.1.3