feat: add 'proof of React' challenge

Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/challenge/preact/preact.go

@@ -0,0 +1,67 @@
+package preact
+
+import (
+	"context"
+	"crypto/subtle"
+	_ "embed"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+
+	"github.com/TecharoHQ/anubis"
+	"github.com/TecharoHQ/anubis/internal"
+	"github.com/TecharoHQ/anubis/lib/challenge"
+	"github.com/TecharoHQ/anubis/lib/localization"
+	"github.com/a-h/templ"
+)
+
+//go:generate ./build.sh
+//go:generate go tool github.com/a-h/templ/cmd/templ generate
+
+//go:embed static/app.js
+var appJS []byte
+
+func renderAppJS(ctx context.Context, out io.Writer) error {
+	fmt.Fprint(out, `<script type="module">`)
+	out.Write(appJS)
+	fmt.Fprint(out, "</script>")
+	return nil
+}
+
+func init() {
+	challenge.Register("preact", &impl{})
+}
+
+type impl struct{}
+
+func (i *impl) Setup(mux *http.ServeMux) {}
+
+func (i *impl) Issue(r *http.Request, lg *slog.Logger, in *challenge.IssueInput) (templ.Component, error) {
+	u, err := r.URL.Parse(anubis.BasePrefix + "/.within.website/x/cmd/anubis/api/pass-challenge")
+	if err != nil {
+		return nil, fmt.Errorf("can't render page: %w", err)
+	}
+
+	q := u.Query()
+	q.Set("redir", r.URL.String())
+	q.Set("id", in.Challenge.ID)
+	u.RawQuery = q.Encode()
+
+	loc := localization.GetLocalizer(r)
+
+	result := page(u.String(), in.Challenge.RandomData, in.Rule.Challenge.Difficulty, loc)
+
+	return result, nil
+}
+
+func (i *impl) Validate(r *http.Request, lg *slog.Logger, in *challenge.ValidateInput) error {
+	got := r.FormValue("result")
+	want := internal.SHA256sum(in.Challenge.RandomData)
+
+	if subtle.ConstantTimeCompare([]byte(want), []byte(got)) != 1 {
+		return challenge.NewError("validate", "invalid response", fmt.Errorf("%w: wanted response %s but got %s", challenge.ErrFailed, want, got))
+	}
+
+	return nil
+}