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.
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.
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.
viaheader 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).