You're mixing old and new API here. request proc from old API (the one that
doesn't use HttpClient) does indeed have extraHeaders parameter. It is,
however, deprecated. The new API tends to pass headers in a client. There is,
however, an option to pass per-request headers to new request proc in current
devel branch:
[https://github.com/nim-lang/Nim/blob/52f20abf22b589bafdf93da024753f71b0e2495b/lib/pure/httpclient.nim#L1003-L1005](https://github.com/nim-lang/Nim/blob/52f20abf22b589bafdf93da024753f71b0e2495b/lib/pure/httpclient.nim#L1003-L1005)
