Proposal: Adding multiple values for Set-Cookie and allowing *http.Cookie type

[linmeii]

Hey, recently I came across an interesting problem.

One of the endpoints in my service needs to return two or more Set-Cookie cookies at the same time.
Currently there is no way to create multiple Set-Cookies at the same time, and any attempt to change the type to an array will raise an error such as:
unsupported type in header: []string

I have two suggestions:

1. Let's add the possibility to apply an array type for the Set-Cookie type header
2. Allow for passing *http.Cookie (and the array) the same as the request comes with *http.Cookie, this would unify the types coming in and out

Example response from documentation

type LoginResponse struct {
	SessionID string `header:"Set-Cookie"`
}

Example request from documentation

type MyAuthParams struct {
	SessionCookie *http.Cookie `cookie:"session"`
}

Example of how I would see the proposal to be integrated:

type Response struct {
	// example param with `header:"Set-Cookie"` as a string
	Cookie string `header:"Set-Cookie"`
	
	// example param with `header:"Set-Cookie"` as a []string
	Cookies []string `header:"Set-Cookie"`
	
	// example param with `header:"Set-Cookie"` as a *http.Cookie
	Cookie *http.Cookie `header:"Set-Cookie"`

        // example param with `header:"Set-Cookie"` as a []*http.Cookie
	 Cookies []*http.Cookie `header:"Set-Cookie"`
}

(obviously only one parameter with header:"Set-Cookie", just an example of multiple different types)