Revert "[GITEA] rework long-term authentication"

This reverts commit 8d2dab94a6.

modules/util/legacy.go

@@ -4,6 +4,10 @@
 package util
 
 import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"errors"
 	"io"
 	"os"
 )
@@ -36,3 +40,52 @@ func CopyFile(src, dest string) error {
 	}
 	return os.Chmod(dest, si.Mode())
 }
+
+// AESGCMEncrypt (from legacy package): encrypts plaintext with the given key using AES in GCM mode. should be replaced.
+func AESGCMEncrypt(key, plaintext []byte) ([]byte, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+
+	nonce := make([]byte, gcm.NonceSize())
+	if _, err := rand.Read(nonce); err != nil {
+		return nil, err
+	}
+
+	ciphertext := gcm.Seal(nil, nonce, plaintext, nil)
+	return append(nonce, ciphertext...), nil
+}
+
+// AESGCMDecrypt (from legacy package): decrypts ciphertext with the given key using AES in GCM mode. should be replaced.
+func AESGCMDecrypt(key, ciphertext []byte) ([]byte, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+
+	size := gcm.NonceSize()
+	if len(ciphertext)-size <= 0 {
+		return nil, errors.New("ciphertext is empty")
+	}
+
+	nonce := ciphertext[:size]
+	ciphertext = ciphertext[size:]
+
+	plainText, err := gcm.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	return plainText, nil
+}