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_th_TH.properties

@@ -572,8 +572,8 @@ login.invalid=ชื่อผู้ใช้หรือรหัสผ่าน
 login.locked=บัญชีของคุณถูกล็อค
 login.signinTitle=กรุณาลงชื่อเข้าใช้
 login.ssoSignIn=เข้าสู่ระบบด้วย Single Sign-on
-login.oauth2AutoCreateDisabled=การสร้างผู้ใช้ OAuth2 อัตโนมัติถูกปิดใช้งาน
-login.oauth2AdminBlockedUser=Registration or logging in of non-registered users is currently blocked. Please contact the administrator.
+login.oAuth2AutoCreateDisabled=การสร้างผู้ใช้ OAuth2 อัตโนมัติถูกปิดใช้งาน
+login.oAuth2AdminBlockedUser=Registration or logging in of non-registered users is currently blocked. Please contact the administrator.
 login.oauth2RequestNotFound=ไม่พบคำขอการอนุญาต
 login.oauth2InvalidUserInfoResponse=การตอบกลับข้อมูลผู้ใช้ไม่ถูกต้อง
 login.oauth2invalidRequest=คำขอไม่ถูกต้อง