Add tests for authentication and security features

- Implement unit tests for password handling in `auth_test.ts`, covering bcrypt and legacy password hashes.
- Create a fake database for user management to facilitate testing of the `AdminHandler`.
- Validate JWT-based identity verification against database records.
- Introduce tests for credential encryption and registry management in `security_test.ts`.
- Ensure registry passwords are securely stored and can be decrypted correctly, including legacy support.
- Add utility functions for password hashing and verification in `auth.ts`.

ts/utils/auth.ts

@@ -0,0 +1,28 @@
+import * as plugins from '../plugins.ts';
+
+const bcryptHashPattern = /^\$2[abxy]\$\d\d\$/;
+
+export function isBcryptHash(passwordHash: string): boolean {
+  return bcryptHashPattern.test(passwordHash);
+}
+
+export function needsPasswordUpgrade(passwordHash: string): boolean {
+  return !isBcryptHash(passwordHash);
+}
+
+export async function hashPassword(password: string): Promise<string> {
+  return await plugins.bcrypt.hash(password);
+}
+
+export async function verifyPassword(password: string, passwordHash: string): Promise<boolean> {
+  if (!passwordHash) {
+    return false;
+  }
+
+  if (isBcryptHash(passwordHash)) {
+    return await plugins.bcrypt.compare(password, passwordHash);
+  }
+
+  // Legacy compatibility for older databases that stored base64-encoded passwords.
+  return passwordHash === btoa(password);
+}