fix: add challenge for HTTP Basic Authentication to container registry (#11678)

After the [first attempt](https://codeberg.org/forgejo/forgejo/pulls/11393) to introduce a separate challenge for HTTP Basic Authentication failed and had to be [backed out](https://codeberg.org/forgejo/forgejo/pulls/11616) because two challenges in a single header field were not widely supported, we're trying it again. This time a second header `WWW-Authenticate` header is emitted.

Example:

```
$ curl -v -u andreas --basic http://192.168.178.62:3000/v2
Enter host password for user 'andreas':
*   Trying 192.168.178.62:3000...
* Connected to 192.168.178.62 (192.168.178.62) port 3000
* using HTTP/1.x
* Server auth using Basic with user 'andreas'
> GET /v2 HTTP/1.1
> Host: 192.168.178.62:3000
> Authorization: Basic *****
> User-Agent: curl/8.15.0
> Accept: */*
>
* Request completely sent off
< HTTP/1.1 401 Unauthorized
< Content-Length: 50
< Content-Type: application/json
< Docker-Distribution-Api-Version: registry/2.0
< Www-Authenticate: Bearer realm="http://192.168.178.62:3000/v2/token",service="container_registry",scope="*"
* Basic authentication problem, ignoring.
< Www-Authenticate: Basic realm="Forgejo Container Registry"
< Date: Sat, 14 Mar 2026 15:09:50 GMT
<
{"errors":[{"code":"UNAUTHORIZED","message":""}]}
```

Tested with Docker 29.1.3, Podman 5.8.0, and Apple container 0.9.0.

## Checklist

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### Tests for Go changes

(can be removed for JavaScript changes)

- I added test coverage for Go changes...
  - [ ] in their respective `*_test.go` for unit tests.
  - [x] in the `tests/integration` directory if it involves interactions with a live Forgejo server.
- I ran...
  - [ ] `make pr-go` before pushing

### Tests for JavaScript changes

(can be removed for Go changes)

- I added test coverage for JavaScript changes...
  - [ ] in `web_src/js/*.test.js` if it can be unit tested.
  - [ ] in `tests/e2e/*.test.e2e.js` if it requires interactions with a live Forgejo server (see also the [developer guide for JavaScript testing](https://codeberg.org/forgejo/forgejo/src/branch/forgejo/tests/e2e/README.md#end-to-end-tests)).

### Documentation

- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [x] I did not document these changes and I do not expect someone else to do it.

### Release notes

- [x] This change will be noticed by a Forgejo user or admin (feature, bug fix, performance, etc.). I suggest to include a release note for this change.
- [ ] This change is not visible to a Forgejo user or admin (refactor, dependency upgrade, etc.). I think there is no need to add a release note for this change.

*The decision if the pull request will be shown in the release notes is up to the mergers / release team.*

The content of the `release-notes/<pull request number>.md` file will serve as the basis for the release notes. If the file does not exist, the title of the pull request will be used instead.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11678
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>
Reviewed-by: Michael Kriese <michael.kriese@gmx.de>
Co-authored-by: Andreas Ahlenstorf <andreas@ahlenstorf.ch>
Co-committed-by: Andreas Ahlenstorf <andreas@ahlenstorf.ch>

tests/integration/api_packages_container_cleanup_sha256_test.go

@@ -63,7 +63,10 @@ func TestPackageContainerCleanupSHA256(t *testing.T) {
 			Token string `json:"token"`
 		}
 
-		authenticate := []string{`Bearer realm="` + setting.AppURL + `v2/token",service="container_registry",scope="*"`}
+		authenticate := []string{
+			`Bearer realm="` + setting.AppURL + `v2/token",service="container_registry",scope="*"`,
+			`Basic realm="Forgejo Container Registry"`,
+		}
 
 		t.Run("User", func(t *testing.T) {
 			req := NewRequest(t, "GET", fmt.Sprintf("%sv2", setting.AppURL))

tests/integration/api_packages_container_test.go

@@ -91,7 +91,10 @@ func TestPackageContainer(t *testing.T) {
 			Token string `json:"token"`
 		}
 
-		authenticate := []string{`Bearer realm="` + setting.AppURL + `v2/token",service="container_registry",scope="*"`}
+		authenticate := []string{
+			`Bearer realm="` + setting.AppURL + `v2/token",service="container_registry",scope="*"`,
+			`Basic realm="Forgejo Container Registry"`,
+		}
 
 		t.Run("Anonymous", func(t *testing.T) {
 			defer tests.PrintCurrentTest(t)()