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/java/stirling/software/SPDF/EE/KeygenLicenseVerifier.java

@@ -20,6 +20,7 @@ import stirling.software.SPDF.utils.GeneralUtils;
 @Service
 @Slf4j
 public class KeygenLicenseVerifier {
+    // todo: place in config files?
     private static final String ACCOUNT_ID = "e5430f69-e834-4ae4-befd-b602aae5f372";
     private static final String BASE_URL = "https://api.keygen.sh/v1/accounts";
     private static final ObjectMapper objectMapper = new ObjectMapper();
@@ -68,7 +69,7 @@ public class KeygenLicenseVerifier {
 
             return false;
         } catch (Exception e) {
-            log.error("Error verifying license: " + e.getMessage());
+            log.error("Error verifying license: {}", e.getMessage());
             return false;
         }
     }
@@ -95,10 +96,9 @@ public class KeygenLicenseVerifier {
                         .build();
 
         HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
-        log.debug(" validateLicenseResponse body: " + response.body());
+        log.debug("ValidateLicenseResponse body: {}", response.body());
         JsonNode jsonResponse = objectMapper.readTree(response.body());
         if (response.statusCode() == 200) {
-
             JsonNode metaNode = jsonResponse.path("meta");
             boolean isValid = metaNode.path("valid").asBoolean();
 
@@ -120,7 +120,7 @@ public class KeygenLicenseVerifier {
             log.info(applicationProperties.toString());
 
         } else {
-            log.error("Error validating license. Status code: " + response.statusCode());
+            log.error("Error validating license. Status code: {}", response.statusCode());
         }
         return jsonResponse;
     }