Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/crypto/crypto.go

@@ -0,0 +1,50 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package crypto // import "miniflux.app/v2/internal/crypto"
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/hex"
+	"fmt"
+
+	"golang.org/x/crypto/bcrypt"
+)
+
+// HashFromBytes returns a SHA-256 checksum of the input.
+func HashFromBytes(value []byte) string {
+	sum := sha256.Sum256(value)
+	return fmt.Sprintf("%x", sum)
+}
+
+// Hash returns a SHA-256 checksum of a string.
+func Hash(value string) string {
+	return HashFromBytes([]byte(value))
+}
+
+// GenerateRandomBytes returns random bytes.
+func GenerateRandomBytes(size int) []byte {
+	b := make([]byte, size)
+	if _, err := rand.Read(b); err != nil {
+		panic(err)
+	}
+
+	return b
+}
+
+// GenerateRandomString returns a random string.
+func GenerateRandomString(size int) string {
+	return base64.URLEncoding.EncodeToString(GenerateRandomBytes(size))
+}
+
+// GenerateRandomStringHex returns a random hexadecimal string.
+func GenerateRandomStringHex(size int) string {
+	return hex.EncodeToString(GenerateRandomBytes(size))
+}
+
+func HashPassword(password string) (string, error) {
+	bytes, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
+	return string(bytes), err
+}