The CORS code has been unmaintained for long time, and the behavior is
not correct.
This PR tries to improve it. The key point is written as comment in
code. And add more tests.
Fix #28515
Fix #27642
Fix #17098
Fix #25473
Although there was `m.Post("/login/oauth/access_token", CorsHandler()...`,
it never really worked, because it still lacks the "OPTIONS" handler.
Replace #25892
Close #21942
Close #25464
Major changes:
1. Serve "robots.txt" and ".well-known/security.txt" in the "public"
custom path
* All files in "public/.well-known" can be served, just like
"public/assets"
3. Add a test for ".well-known/security.txt"
4. Simplify the "FileHandlerFunc" logic, now the paths are consistent so
the code can be simpler
5. Add CORS header for ".well-known" endpoints
6. Add logs to tell users they should move some of their legacy custom
public files
```
2023/07/19 13:00:37 cmd/web.go:178:serveInstalled() [E] Found legacy public asset "img" in CustomPath. Please move it to /work/gitea/custom/public/assets/img
2023/07/19 13:00:37 cmd/web.go:182:serveInstalled() [E] Found legacy public asset "robots.txt" in CustomPath. Please move it to /work/gitea/custom/public/robots.txt
```
This PR is not breaking.
---------
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Giteabot <teabot@gitea.io>
`http.ServeFile/ServeContent` handles `If-xxx`, `Content-Length`,
`Range` and `Etag` correctly
After this PR, storage files (eg: avatar) could be responded with
correct Content-Length.
