Set more than one cookie in the 'Set-Cookie' header in a cloudflare worker header.set('Set-Cookie' function

I'm trying to use a cloudfare worker to add 2 cookie key/value pairs to the response before sending it to the client.

Unfortunately all documentation for the cloudflare workers says to use the response.headers.set('Set-Cookie',xxx) function to set the cookie value:

let response = await fetch(request);
response = new Response(response.body, response);

response.headers.set('Set-Cookie', "val1=x; Expires=Wed, 21 Oct 2020 07:28:00 GMT; Path='/';");

return response;

This only allows you to set one cookie header, and if called twice just overwrites the existing header.

I have tried calling the function twice, only the last value comes in:

response.headers.set('Set-Cookie', "val1=1; Expires=Wed, 21 Oct 2020 07:28:00 GMT; Path='/';");
response.headers.set('Set-Cookie', "val2=2; Expires=Wed, 21 Oct 2020 07:28:00 GMT; Path='/';");

I have tried passing 2 cookies in the one header, separated with a comma, but only one comes in:

response.headers.set('Set-Cookie', "val1=1; Expires=Wed, 21 Oct 2020 07:28:00 GMT; Path='/';, val2=2; Expires=Wed, 21 Oct 2020 07:28:00 GMT; Path='/';");

I have tried passing 2 cookie key/value pairs, but the first key value is set to "1, val2=2":

response.headers.set('Set-Cookie', "val1=1, val2=2; Expires=Wed, 21 Oct 2020 07:28:00 GMT; Path='/';");

None of these work.

The only work around I have found is to bundle the vars up into one variable, and then use JS on the client side to unpack and apply the variable:

response.headers.set('Set-Cookie', "jsVal={val1:1, val2:2}; Expires=Wed, 21 Oct 2020 07:28:00 GMT; Path='/';");

.. and then in a js file apply the 2 cookie values. Obviously this is not ideal.

Has anyone had any luck applying 2 separate cookies in one response header via a cloudflare worker? Thanks.