add jwt creating and parsing

internal/jwt/parse.go

@@ -0,0 +1,28 @@
+package jwt
+
+import (
+	"fmt"
+
+	"github.com/golang-jwt/jwt/v5"
+)
+
+func parse(
+	tokenStr string,
+	method jwt.SigningMethod,
+	key any,
+) (jwt.Claims, error) {
+	t, err := jwt.Parse(tokenStr, func(tok *jwt.Token) (any, error) {
+		if tok.Method.Alg() != method.Alg() {
+			return nil, fmt.Errorf("unexpected signing method")
+		}
+		return key, nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	// check validity twice: invalid token may return nil error
+	if !t.Valid {
+		return nil, fmt.Errorf("invalid token")
+	}
+	return t.Claims, nil
+}