Implements api routes and api key auth

CAUTION: Temporary api key is hardcoded, must be changed

internal/api/auth.go

@@ -0,0 +1,54 @@
+package api
+
+import (
+	"crypto/sha256"
+	"crypto/subtle"
+	"regexp"
+	"strings"
+
+	"github.com/gofiber/fiber/v2"
+	"github.com/gofiber/fiber/v2/middleware/keyauth"
+)
+
+var (
+	apiKey        = "willbechanged"
+	protectedURLs = []*regexp.Regexp{
+		regexp.MustCompile("^/api$"),
+	}
+	errForbidden = &fiber.Error{
+		Code:    403,
+		Message: "API Key is missing or invalid",
+	}
+)
+
+func validateAPIKey(_ *fiber.Ctx, key string) (bool, error) {
+	hashedAPIKey := sha256.Sum256([]byte(apiKey))
+	hashedKey := sha256.Sum256([]byte(key))
+
+	if subtle.ConstantTimeCompare(hashedAPIKey[:], hashedKey[:]) == 1 {
+		return true, nil
+	}
+
+	return false, keyauth.ErrMissingOrMalformedAPIKey
+}
+
+func protectedRoutesFilter(ctx *fiber.Ctx) bool {
+	originalURL := strings.ToLower(ctx.OriginalURL())
+
+	for _, pattern := range protectedURLs {
+		if pattern.MatchString(originalURL) {
+			return false
+		}
+	}
+	return true
+}
+
+func successHandler(ctx *fiber.Ctx) error {
+	return ctx.Next()
+}
+
+func errHandler(ctx *fiber.Ctx, err error) error {
+	ctx.Status(fiber.StatusForbidden)
+
+	return ctx.JSON(errForbidden)
+}