Multiple `Set-Cookie` headers?

[Sam]

Is there any way I can set multiple Set-Cookie headers? Currently if I do the following, only the last item in the array, b=b, is set:

handler(request, response, {
  public: "public",
  headers: [
    {
      source: "**",
      headers: [
        {
          key: "Set-Cookie",
          value: `a=a`
        },
        {
          key: "Set-Cookie",
          value: `b=b`
        }
      ]
    }
  ]
});