- https://www.w3.org/Protocols/rfc2616/rfc2616-sec2.html#sec2.2 <header name>
- https://specs.openstack.org/openstack/api-wg/guidelines/headers.html
- https://www.keycdn.com/support/custom-http-headers
- https://stackoverflow.com/questions/22856136/why-underscores-are-forbidden-in-http-header-names
- https://devcentral.f5.com/questions/how-to-allow-underscore-in-http-header-47814