Enhance SSO SAML in desktop app (#5705)

# Description of Changes
Change the SAML support for SSO to understand when a request is coming
from the desktop app, and use the alternate auth flow that the desktop
app requires.

app/proprietary/src/main/java/stirling/software/proprietary/security/saml2/CustomSaml2AuthenticationFailureHandler.java

@@ -17,6 +17,7 @@ import lombok.extern.slf4j.Slf4j;
 import stirling.software.proprietary.audit.AuditEventType;
 import stirling.software.proprietary.audit.AuditLevel;
 import stirling.software.proprietary.audit.Audited;
+import stirling.software.proprietary.security.oauth2.TauriOAuthUtils;
 
 @Slf4j
 @ConditionalOnProperty(name = "security.saml2.enabled", havingValue = "true")
@@ -33,9 +34,33 @@ public class CustomSaml2AuthenticationFailureHandler extends SimpleUrlAuthentica
 
         if (exception instanceof Saml2AuthenticationException) {
             Saml2Error error = ((Saml2AuthenticationException) exception).getSaml2Error();
+            if (TauriSamlUtils.isTauriRelayState(request)) {
+                String redirectUrl =
+                        TauriOAuthUtils.defaultTauriCallbackPath(request.getContextPath());
+                String nonce = TauriSamlUtils.extractNonceFromRequest(request);
+                if (nonce != null) {
+                    redirectUrl = appendQueryParam(redirectUrl, "nonce", nonce);
+                }
+                redirectUrl = appendQueryParam(redirectUrl, "errorOAuth", error.getErrorCode());
+                getRedirectStrategy().sendRedirect(request, response, redirectUrl);
+                return;
+            }
             getRedirectStrategy()
                     .sendRedirect(request, response, "/login?errorOAuth=" + error.getErrorCode());
         } else if (exception instanceof ProviderNotFoundException) {
+            if (TauriSamlUtils.isTauriRelayState(request)) {
+                String redirectUrl =
+                        TauriOAuthUtils.defaultTauriCallbackPath(request.getContextPath());
+                String nonce = TauriSamlUtils.extractNonceFromRequest(request);
+                if (nonce != null) {
+                    redirectUrl = appendQueryParam(redirectUrl, "nonce", nonce);
+                }
+                redirectUrl =
+                        appendQueryParam(
+                                redirectUrl, "errorOAuth", "not_authentication_provider_found");
+                getRedirectStrategy().sendRedirect(request, response, redirectUrl);
+                return;
+            }
             getRedirectStrategy()
                     .sendRedirect(
                             request,
@@ -43,4 +68,19 @@ public class CustomSaml2AuthenticationFailureHandler extends SimpleUrlAuthentica
                             "/login?errorOAuth=not_authentication_provider_found");
         }
     }
+
+    private String appendQueryParam(String path, String key, String value) {
+        if (path == null || path.isBlank()) {
+            return path;
+        }
+        String separator = path.contains("?") ? "&" : "?";
+        String encodedKey =
+                java.net.URLEncoder.encode(key, java.nio.charset.StandardCharsets.UTF_8);
+        String encodedValue =
+                value == null
+                        ? ""
+                        : java.net.URLEncoder.encode(
+                                value, java.nio.charset.StandardCharsets.UTF_8);
+        return path + separator + encodedKey + "=" + encodedValue;
+    }
 }

app/proprietary/src/main/java/stirling/software/proprietary/security/saml2/CustomSaml2AuthenticationSuccessHandler.java

@@ -33,6 +33,7 @@ import stirling.software.proprietary.audit.AuditEventType;
 import stirling.software.proprietary.audit.AuditLevel;
 import stirling.software.proprietary.audit.Audited;
 import stirling.software.proprietary.security.model.AuthenticationType;
+import stirling.software.proprietary.security.oauth2.TauriOAuthUtils;
 import stirling.software.proprietary.security.service.JwtServiceInterface;
 import stirling.software.proprietary.security.service.LoginAttemptService;
 import stirling.software.proprietary.security.service.UserService;
@@ -233,7 +234,16 @@ public class CustomSaml2AuthenticationSuccessHandler
         String redirectPath = resolveRedirectPath(request, contextPath);
         String origin = resolveOrigin(request);
         clearRedirectCookie(response);
-        return origin + redirectPath + "#access_token=" + jwt;
+        String url = origin + redirectPath + "#access_token=" + jwt;
+
+        String nonce = TauriSamlUtils.extractNonceFromRequest(request);
+        if (nonce != null) {
+            url +=
+                    "&nonce="
+                            + java.net.URLEncoder.encode(
+                                    nonce, java.nio.charset.StandardCharsets.UTF_8);
+        }
+        return url;
     }
 
     /**
@@ -256,6 +266,9 @@ public class CustomSaml2AuthenticationSuccessHandler
     }
 
     private String resolveRedirectPath(HttpServletRequest request, String contextPath) {
+        if (TauriSamlUtils.isTauriRelayState(request)) {
+            return TauriOAuthUtils.defaultTauriCallbackPath(contextPath);
+        }
         return extractRedirectPathFromCookie(request)
                 .filter(path -> path.startsWith("/"))
                 .orElseGet(() -> defaultCallbackPath(contextPath));

app/proprietary/src/main/java/stirling/software/proprietary/security/saml2/Saml2Configuration.java

@@ -156,6 +156,16 @@ public class Saml2Configuration {
         OpenSaml4AuthenticationRequestResolver resolver =
                 new OpenSaml4AuthenticationRequestResolver(relyingPartyRegistrationRepository);
 
+        resolver.setRelayStateResolver(
+                request -> {
+                    String tauriParam = request.getParameter("tauri");
+                    if (!"1".equals(tauriParam)) {
+                        return null;
+                    }
+                    String nonce = request.getParameter("nonce");
+                    return TauriSamlUtils.buildRelayState(nonce);
+                });
+
         resolver.setAuthnRequestCustomizer(
                 customizer -> {
                     HttpServletRequest request = customizer.getRequest();

app/proprietary/src/main/java/stirling/software/proprietary/security/saml2/TauriSamlUtils.java

@@ -0,0 +1,42 @@
+package stirling.software.proprietary.security.saml2;
+
+import jakarta.servlet.http.HttpServletRequest;
+
+/** Utility helpers for the Tauri desktop SAML flow. */
+public final class TauriSamlUtils {
+
+    public static final String TAURI_RELAY_STATE_PREFIX = "tauri:";
+
+    private TauriSamlUtils() {
+        // Utility class - prevent instantiation
+    }
+
+    public static boolean isTauriRelayState(HttpServletRequest request) {
+        String relayState = request.getParameter("RelayState");
+        return relayState != null
+                && (relayState.equals("tauri") || relayState.startsWith(TAURI_RELAY_STATE_PREFIX));
+    }
+
+    public static String extractNonceFromRelayState(String relayState) {
+        if (relayState == null || !relayState.startsWith(TAURI_RELAY_STATE_PREFIX)) {
+            return null;
+        }
+        String[] parts = relayState.split(":");
+        if (parts.length >= 2) {
+            String nonce = parts[parts.length - 1];
+            return nonce.isBlank() ? null : nonce;
+        }
+        return null;
+    }
+
+    public static String extractNonceFromRequest(HttpServletRequest request) {
+        return extractNonceFromRelayState(request.getParameter("RelayState"));
+    }
+
+    public static String buildRelayState(String nonce) {
+        if (nonce == null || nonce.isBlank()) {
+            return "tauri";
+        }
+        return TAURI_RELAY_STATE_PREFIX + nonce;
+    }
+}