org.http4s.headers

 The "Accept-Charset" header field can be sent by a user agent to
 indicate what charsets are acceptable in textual response content.
 This field allows user agents capable of understanding more

From [https://datatracker.ietf.org/doc/html/rfc7231#section-5.3.3 RFC-7231].

Request header used to indicate which natural language would be preferred for the response to be translated into.

RFC-7231 Section 5.3.5

The Access-Control-Allow-Methods header.

The Access-Control-Max-Age header.

Constructs an Age header.

The value of this field is a positive number of seconds (in decimal) with an estimate of the amount of time since the response

A Response header that lists the methods that are supported by the target resource. Must be attached to responses with status 405 Not Allowed, though in practice not all servers honor this.

RFC-7231 Section 7.4.1 Allow

Constructs a Content-Length header.

The HTTP RFCs do not specify a maximum length. We have decided that Long.MaxValue bytes ought to be good enough for anybody in order to avoid the irritations of BigInt.

 The "Content-Location" header field references a URI that can be used
 as an identifier for a specific resource corresponding to the
 representation in this message's payload

RFC-7231 Section 3.1.4.2

 The "Content-Type" header field indicates the media type of the
 associated representation: either the representation enclosed in the
 message payload or the selected representation, as determined by the
 message semantics.

RFC-7231

This response header conveys a desire that the browser blocks no-cors cross-origin/cross-site requests to the given resource

Deprecation Header

https://greenbytes.de/tech/webdav/draft-ietf-httpapi-deprecation-header-latest.html#the-deprecation-http-response-header-field

A Response header that gives the date/time after which the response is considered stale.

The HTTP RFCs indicate that Expires should be in the range of now to 1 year in the future. However, it is a usual practice to set it to the past of far in the future Thus any instant is in practice allowed

RFC-7234 Section 5.3

A Request header, that provides the host and port information

 The "Host" header field in a request provides the host and port
 information from the target URI, enabling the origin server to
 distinguish among resources while servicing requests for multiple
 host names on a single IP address.

This header was mandatory in version 1.1 of the Http protocol.

RFC-7230 Section 5.4

Request header defines request to be idempotent used by client retry middleware.

idempotency-header

Request header to make the request conditional on the current contents of the origin server at the given target resource (URI).

RFC-7232 Section 3.1

{{ The "If-Modified-Since" header field makes a GET or HEAD request method conditional on the selected representation's modification date being more recent than the date provided in the field-value. }}

RFC-7232

The "If-None-Match" header field makes the request method conditional
on a recipient cache or origin server either not having any current
representation of the target resource, when the field-value is "*",
or having a selected representation with an entity-tag that does not
match any of those listed in the field-value.

From RFC-7232

Response header that indicates the time at which the server believes the entity was last modified.

RFC-7232

Request header, used with the TRACE and OPTION request methods, that gives an upper bound on how many times the request can be forwarded by a proxy before it is rejected.

RFC-7231

 The "Proxy-Authenticate" header field consists of at least one
 challenge that indicates the authentication scheme(s) and parameters
 applicable to the proxy for this effective request URI...

From RFC-7235

 The "Proxy-Authorization" header field allows the client to identify
 itself (or its user) to a proxy that requires authentication.

From RFC-7235

Response header, used by the server to indicate to the user-agent how long it has to wait before it can try again with a follow-up request.

RFC-7231 Section 7.1.3

Server header https://datatracker.ietf.org/doc/html/rfc7231#section-7.4.2

A Response header that links generated code to a source map, enabling the browser to reconstruct the original source and present the reconstructed original in the debugger.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/SourceMap

Defined by https://datatracker.ietf.org/doc/html/rfc6797

Sunset Header - RFC 8594

https://www.rfc-editor.org/rfc/rfc8594

User-Agent header RFC-7231 Section 5.5.3