SSO Refactoring (#2818)

# Description of Changes

* Refactoring of SSO code around OAuth & SAML 2
* Enabling auto-login with SAML 2 via the new `SSOAutoLogin` property
* Correcting typos & general cleanup

---

## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md)
(if applicable)
- [x] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] My changes generate no new warnings

### Documentation

- [x] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [x] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [x] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#6-testing)
for more details.

src/main/resources/messages_zh_TW.properties

@@ -572,8 +572,8 @@ login.invalid=使用者名稱或密碼無效。
 login.locked=您的帳號已被鎖定。
 login.signinTitle=請登入
 login.ssoSignIn=透過 SSO 單一登入
-login.oauth2AutoCreateDisabled=OAuth 2.0 自動建立使用者功能已停用
-login.oauth2AdminBlockedUser=目前不允許未註冊的使用者註冊或登入。請聯絡系統管理員。
+login.oAuth2AutoCreateDisabled=OAuth 2.0 自動建立使用者功能已停用
+login.oAuth2AdminBlockedUser=目前不允許未註冊的使用者註冊或登入。請聯絡系統管理員。
 login.oauth2RequestNotFound=找不到驗證請求
 login.oauth2InvalidUserInfoResponse=使用者資訊回應無效
 login.oauth2invalidRequest=請求無效