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/controller/api/UserController.java

@@ -36,7 +36,7 @@ import stirling.software.SPDF.model.AuthenticationType;
 import stirling.software.SPDF.model.Role;
 import stirling.software.SPDF.model.User;
 import stirling.software.SPDF.model.api.user.UsernameAndPass;
-import stirling.software.SPDF.model.provider.UnsupportedProviderException;
+import stirling.software.SPDF.model.exception.UnsupportedProviderException;
 
 @Controller
 @Tag(name = "User", description = "User APIs")
@@ -126,7 +126,7 @@ public class UserController {
             return new RedirectView("/change-creds?messageType=notAuthenticated", true);
         }
         Optional<User> userOpt = userService.findByUsernameIgnoreCase(principal.getName());
-        if (userOpt == null || userOpt.isEmpty()) {
+        if (userOpt.isEmpty()) {
             return new RedirectView("/change-creds?messageType=userNotFound", true);
         }
         User user = userOpt.get();
@@ -154,7 +154,7 @@ public class UserController {
             return new RedirectView("/account?messageType=notAuthenticated", true);
         }
         Optional<User> userOpt = userService.findByUsernameIgnoreCase(principal.getName());
-        if (userOpt == null || userOpt.isEmpty()) {
+        if (userOpt.isEmpty()) {
             return new RedirectView("/account?messageType=userNotFound", true);
         }
         User user = userOpt.get();
@@ -176,7 +176,7 @@ public class UserController {
         for (Map.Entry<String, String[]> entry : paramMap.entrySet()) {
             updates.put(entry.getKey(), entry.getValue()[0]);
         }
-        log.debug("Processed updates: " + updates);
+        log.debug("Processed updates: {}", updates);
         // Assuming you have a method in userService to update the settings for a user
         userService.updateUserSettings(principal.getName(), updates);
         // Redirect to a page of your choice after updating
@@ -199,7 +199,7 @@ public class UserController {
         Optional<User> userOpt = userService.findByUsernameIgnoreCase(username);
         if (userOpt.isPresent()) {
             User user = userOpt.get();
-            if (user != null && user.getUsername().equalsIgnoreCase(username)) {
+            if (user.getUsername().equalsIgnoreCase(username)) {
                 return new RedirectView("/addUsers?messageType=usernameExists", true);
             }
         }
@@ -276,7 +276,7 @@ public class UserController {
             Authentication authentication)
             throws SQLException, UnsupportedProviderException {
         Optional<User> userOpt = userService.findByUsernameIgnoreCase(username);
-        if (!userOpt.isPresent()) {
+        if (userOpt.isEmpty()) {
             return new RedirectView("/addUsers?messageType=userNotFound", true);
         }
         if (!userService.usernameExistsIgnoreCase(username)) {
@@ -295,20 +295,20 @@ public class UserController {
             List<Object> principals = sessionRegistry.getAllPrincipals();
             String userNameP = "";
             for (Object principal : principals) {
-                List<SessionInformation> sessionsInformations =
+                List<SessionInformation> sessionsInformation =
                         sessionRegistry.getAllSessions(principal, false);
                 if (principal instanceof UserDetails) {
                     userNameP = ((UserDetails) principal).getUsername();
                 } else if (principal instanceof OAuth2User) {
                     userNameP = ((OAuth2User) principal).getName();
                 } else if (principal instanceof CustomSaml2AuthenticatedPrincipal) {
-                    userNameP = ((CustomSaml2AuthenticatedPrincipal) principal).getName();
+                    userNameP = ((CustomSaml2AuthenticatedPrincipal) principal).name();
                 } else if (principal instanceof String) {
                     userNameP = (String) principal;
                 }
                 if (userNameP.equalsIgnoreCase(username)) {
-                    for (SessionInformation sessionsInformation : sessionsInformations) {
-                        sessionRegistry.expireSession(sessionsInformation.getSessionId());
+                    for (SessionInformation sessionInfo : sessionsInformation) {
+                        sessionRegistry.expireSession(sessionInfo.getSessionId());
                     }
                 }
             }