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How to link two domains using HTTP Via headers domain hashes

HTTP requests and responses can contain a number of extra headers, which you can use to send along extra metadata about the server serving the request.

Carbon.txt supports using the HTTP Via header, to declare that a HTTP response has been sent along by one or more intermediate entities. In our case usually a managed hosting provider.

  1. Follow the steps above to create your carbon.txt file

    Follow Steps 1 to 4 of the Getting Started guide above to create a carbon.txt file for your organisation.

  2. Create a domain hash for the domain you want to show as green

    Create a domain hash. This is a SHA256 hash of your shared secret and the domain you want to establish a link to.

    Use the form below to create one.

    Green Web Foundation credentials:

  3. Set the via header on HTTP responses to requests for the domain you want to show as green

    For example: my-org.com also owns me.my-org.com. In order to link me.my-org.com to the main carbon.txt file, when a request comes in for me.my-org.com, you would configure the server serving the request to add the following Via header.

    Via: 1.1 https://my-org.com/carbon.txt <generated_domain_hash>

    Note: the domain hash would be a 64 character hash of me.my-org.com and your shared secret.

    We maintain a set of server config setup examples folder on github, for popular open source servers like Nginx, Caddy, Apache, and so on (pull requests gratefully accepted).