[PM-1632] Redirect on SsoRequired - return SsoOrganizationIdentifier (#6597)

feat: add SSO request validation and organization identifier lookup

- Implement SsoRequestValidator to validate SSO requirements
- Add UserSsoOrganizationIdentifierQuery to fetch organization identifiers
- Create SsoOrganizationIdentifier custom response for SSO redirects
- Add feature flag (RedirectOnSsoRequired) for gradual rollout
- Register validators and queries in dependency injection
- Create RequestValidationConstants to reduce magic strings
- Add comprehensive test coverage for validation logic
- Update BaseRequestValidator to consume SsoRequestValidator

src/Core/Auth/UserFeatures/UserServiceCollectionExtensions.cs

@@ -1,5 +1,4 @@
-
-
+using Bit.Core.Auth.Sso;
 using Bit.Core.Auth.UserFeatures.DeviceTrust;
 using Bit.Core.Auth.UserFeatures.Registration;
 using Bit.Core.Auth.UserFeatures.Registration.Implementations;
@@ -29,6 +28,7 @@ public static class UserServiceCollectionExtensions
         services.AddWebAuthnLoginCommands();
         services.AddTdeOffboardingPasswordCommands();
         services.AddTwoFactorQueries();
+        services.AddSsoQueries();
     }
 
     public static void AddDeviceTrustCommands(this IServiceCollection services)
@@ -69,4 +69,9 @@ public static class UserServiceCollectionExtensions
     {
         services.AddScoped<ITwoFactorIsEnabledQuery, TwoFactorIsEnabledQuery>();
     }
+
+    private static void AddSsoQueries(this IServiceCollection services)
+    {
+        services.AddScoped<IUserSsoOrganizationIdentifierQuery, UserSsoOrganizationIdentifierQuery>();
+    }
 }