Response cookies must be set using cowboy_req

[eric0fw]

Response cookies must be set using cowboy_req

[essen]

Yes this is due to Cowboy being more explicit in what is not allowed with regard to the set-cookie header. Setting it the way Plug does is wrong because the set-cookie header is special (it breaks the HTTP spec) and Cowboy cannot handle it like other headers. That it happened to work before is a coincidence and it likely could break in various ways. So the solution is to either use the appropriate functions or to set the resp_cookies value directly in the Req.

I don't know what needs to happen in Plug or Phoenix or other projects to make things work as I don't do Elixir. But both solutions above should work for all versions 2.x and probably even 1.x as well.