Have an "allows-headers" field

[krainboltgreene]

This would tell the client what headers they allow:

{
  "allows-headers": {
    "Accept": ["application/json", "application/vnd.api+json", "*/*"],
    "Content-Type": ["application/vnd.api+json"],
    "Authorization": [null, "Bearer"]
  }
}

[krainboltgreene]

Values: String|Array<String>|Map<String, String|Array<String>>

For example the Content-Type header has "options":

"Content-Type": {
  "application/vnd.api+json": {
    "charset": "utf-8"
  }
}

Which would match:

Content-Type: application/vnd.api+json; charset=utf-8