APIcast is unable to validate JWT token if the content-type of jwks_uri isn't "application/json"

Issue

• APIcast is unable to validate JWT token, it logs No trusted certs loaded.

  2021/01/01 00:00:00 [debug] 19#19: *45402 oidc.lua:191: verify(): [jwt] failed verification for token, reason: No trusted certs loaded, requestID=xxxxx
  2021/01/01 00:00:00 [debug] 19#19: *45402 proxy.lua:280: rewrite(): oauth failed with No trusted certs loaded, requestID=xxxxx
  

  However, my JWKS is reachable from the apicast.

  sh-4.4$ curl -v https://sso.example.com/jwks.json
  ....
  < HTTP/1.1 200 200
  < Date: Mon, 01 Jan 2021 00:00:00 GMT
  < Server: Apache
  < Access-Control-Allow-Origin: *
  < Access-Control-Allow-Credentials: true
  < Access-Control-Allow-Headers: Content-Type, Access-Control-Allow-Headers, Authorization, X-Requested-With
  < Access-Control-Allow-Methods: GET,POST,OPTIONS
  < Cache-Control: no-store
  < Pragma: no-cache
  < Content-Length: 900
  < Content-Type: application/jwk-set+json;charset=UTF-8
  < 
  * Connection #0 to host sso.example.com left intact
  {"keys":[{"kty":"RSA","e":"AQAB","use":"sig","kid":"......