How to respond with multiple Set-Cookie header?

[SolaWing]

according to https://tools.ietf.org/html/rfc6265#section-3

An origin server can include multiple Set-Cookie header fields in a single response

I can use raw to set headers, but header dictionary override old Set-Cookie key

[inigo333]

Any updates on this? Shouldn't the type for the response header be [(String, String)]? instead of [String : String]? ?