set CORS on .well-known URI to unbreak modular

[ara4n]

otherwise a riot/web running on foo.riot.im can't query the .well-known on foo.modular.im...

[richvdh]

fixes #4593 I guess?

[ara4n]

yup

[richvdh]

can has changelog entry pls? lgtm otherwise

[richvdh]

oh, except for the bit where all the CI is failing because you haven't imported set_cors_headers

[richvdh]

lgtm once you fix the CI

[codecov-io]

Codecov Report

Merging #4651 into develop will decrease coverage by 0.01%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop    #4651      +/-   ##
===========================================
- Coverage    75.23%   75.22%   -0.02%     
===========================================
  Files          338      338              
  Lines        34581    34653      +72     
  Branches      5655     5678      +23     
===========================================
+ Hits         26018    26067      +49     
- Misses        6971     6991      +20     
- Partials      1592     1595       +3

[n1trux]

If you get a 404, the header isn't set, which breaks Riot, for example.

Excerpt from my Chrome network log:

GET https://synapse.example.org/_matrix/identity/api/v1 404
Access to XMLHttpRequest at 'https://synapse.example.org/_matrix/identity/api/v1' from origin 'https://chat.example.org' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

Related: #1595