Add Access-Control-Allow-Origin to .well-known/matrix/client response

[jo-so]

Description:

It would be helpful, if the response of .well-known/matrix/client contains the field Access-Control-Allow-Origin: *. Currently, I have to add this with Nginx to make the login of riot.im/staging work.

% nc -C ip6-localhost 8008 <<<$'GET /.well-known/matrix/client HTTP/1.0\n'
HTTP/1.0 200 OK
Content-Length: 55
Date: Fri, 08 Feb 2019 21:43:44 GMT
Content-Type: application/json
Server: Synapse/0.34.1.1

{"m.homeserver": {"base_url": "https://alea.gnuu.de/"}}

[turt2live]

Related: element-hq/element-web#7760

[n1trux]

This was apparently fixed in #4651 but if you get a 404 code the Access-Control-Allow-Origin header isn't set, which leads to other errors.

Related: #1595

[richvdh]

fixed by #4651