Add authentication function

Signed-off-by: Asai Neko <sugar@sne.moe>

pkgs/turnstile/turnstile.go

@@ -0,0 +1,34 @@
+package turnstile
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/url"
+
+	"github.com/spf13/viper"
+)
+
+func VerifyTurnstile(token, ip string) (bool, error) {
+	form := url.Values{}
+	form.Set("secret", viper.GetString("secrets.turnstile"))
+	form.Set("response", token)
+	form.Set("remoteip", ip)
+
+	resp, err := http.PostForm(
+		"https://challenges.cloudflare.com/turnstile/v0/siteverify",
+		form,
+	)
+	if err != nil {
+		return false, err
+	}
+	defer resp.Body.Close()
+
+	var result struct {
+		Success bool `json:"success"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
+		return false, err
+	}
+
+	return result.Success, nil
+}