Give API error responses in JSON format

[Kevinjil]

Description of the enhancement request

Currently, a 404 on an API endpoints gives a HTML page back. This is both wasteful in rendering and annoying to parse on the client / CLI.

The goal you want to achieve

For endpoints which normally return JSON, also return JSON in the non-happy flow.

[nickygerritsen]

On demoweb it DOES produce JSON:

curl -v https://www.domjudge.org/demoweb/api/contests/test
* Host www.domjudge.org:443 was resolved.
* IPv6: (none)
* IPv4: 192.87.110.101
*   Trying 192.87.110.101:443...
* Connected to www.domjudge.org (192.87.110.101) port 443
* ALPN: curl offers h2,http/1.1
* (304) (OUT), TLS handshake, Client hello (1):
*  CAfile: /etc/ssl/cert.pem
*  CApath: none
* (304) (IN), TLS handshake, Server hello (2):
* (304) (IN), TLS handshake, Unknown (8):
* (304) (IN), TLS handshake, Certificate (11):
* (304) (IN), TLS handshake, CERT verify (15):
* (304) (IN), TLS handshake, Finished (20):
* (304) (OUT), TLS handshake, Finished (20):
* SSL connection using TLSv1.3 / AEAD-AES256-GCM-SHA384 / [blank] / UNDEF
* ALPN: server accepted h2
* Server certificate:
*  subject: CN=www.domjudge.org
*  start date: Sep 10 18:18:43 2024 GMT
*  expire date: Dec  9 18:18:42 2024 GMT
*  subjectAltName: host "www.domjudge.org" matched cert's "www.domjudge.org"
*  issuer: C=US; O=Let's Encrypt; CN=R10
*  SSL certificate verify ok.
* using HTTP/2
* [HTTP/2] [1] OPENED stream for https://www.domjudge.org/demoweb/api/contests/test
* [HTTP/2] [1] [:method: GET]
* [HTTP/2] [1] [:scheme: https]
* [HTTP/2] [1] [:authority: www.domjudge.org]
* [HTTP/2] [1] [:path: /demoweb/api/contests/test]
* [HTTP/2] [1] [user-agent: curl/8.7.1]
* [HTTP/2] [1] [accept: */*]
> GET /demoweb/api/contests/test HTTP/2
> Host: www.domjudge.org
> User-Agent: curl/8.7.1
> Accept: */*
>
* Request completely sent off
< HTTP/2 404
< vary: Accept
< cache-control: max-age=0, must-revalidate, private
< date: Sun, 15 Sep 2024 04:49:15 GMT
< content-security-policy: default-src 'self'; style-src 'self' 'unsafe-inline' https://cdn.jsdelivr.net; script-src 'self' 'unsafe-inline' https://cdn.jsdelivr.net; img-src 'self' data: secure.gravatar.com
< x-current-contest:
< expires: Sun, 15 Sep 2024 04:49:15 GMT
< referrer-policy: strict-origin-when-cross-origin
< strict-transport-security: max-age=31556952
< x-content-type-options: nosniff
< x-xss-protection: 1; mode=block
< x-frame-options: DENY
< x-frame-options: DENY
< referrer-policy: same-origin
< x-content-type-options: nosniff
< x-xss-protection: 1; mode=block
< content-type: application/json
< server: Apache/2.4.61 (Debian)
<
* Connection #0 to host www.domjudge.org left intact
{"code":404,"message":"Object with ID 'test' not found"}%

So maybe this is either specific endpoints or only happening in dev-mode?