Introduce Spam protection

fixes #1958

Adds 2 new options:
* Do not allow stores to use the email settings of the server. Instead, they would need to fill in the email settings in their own store
* Do not allow user creation through the API unless you are an admin.

Both are opt-in and turned off by default.

BTCPayServer/Controllers/GreenField/UsersController.cs

@@ -8,6 +8,7 @@ using BTCPayServer.Client.Models;
 using BTCPayServer.Configuration;
 using BTCPayServer.Data;
 using BTCPayServer.Events;
+using BTCPayServer.HostedServices;
 using BTCPayServer.Logging;
 using BTCPayServer.Security;
 using BTCPayServer.Security.GreenField;
@@ -35,6 +36,7 @@ namespace BTCPayServer.Controllers.GreenField
         private readonly RateLimitService _throttleService;
         private readonly BTCPayServerOptions _options;
         private readonly IAuthorizationService _authorizationService;
+        private readonly CssThemeManager _themeManager;
 
         public UsersController(UserManager<ApplicationUser> userManager, BTCPayServerOptions btcPayServerOptions,
             RoleManager<IdentityRole> roleManager, SettingsRepository settingsRepository,
@@ -42,7 +44,8 @@ namespace BTCPayServer.Controllers.GreenField
             IPasswordValidator<ApplicationUser> passwordValidator,
             RateLimitService throttleService,
             BTCPayServerOptions options,
-            IAuthorizationService authorizationService)
+            IAuthorizationService authorizationService,
+            CssThemeManager themeManager)
         {
             _userManager = userManager;
             _btcPayServerOptions = btcPayServerOptions;
@@ -53,6 +56,7 @@ namespace BTCPayServer.Controllers.GreenField
             _throttleService = throttleService;
             _options = options;
             _authorizationService = authorizationService;
+            _themeManager = themeManager;
         }
 
         [Authorize(Policy = Policies.CanViewProfile, AuthenticationSchemes = AuthenticationSchemes.Greenfield)]
@@ -100,7 +104,7 @@ namespace BTCPayServer.Controllers.GreenField
             if (request.IsAdministrator is true && !isAdmin)
                 return Forbid(AuthenticationSchemes.GreenfieldBasic);
 
-            if (!isAdmin && policies.LockSubscription)
+            if (!isAdmin && (policies.LockSubscription || _themeManager.Policies.DisableUnauthenticatedUserApi))
             {
                 // If we are not admin and subscriptions are locked, we need to check the Policies.CanCreateUser.Key permission
                 var canCreateUser = (await _authorizationService.AuthorizeAsync(User, null, new PolicyRequirement(Policies.CanCreateUser))).Succeeded;

BTCPayServer/Services/Mails/EmailSenderFactory.cs

@@ -1,28 +1,34 @@
+using BTCPayServer.HostedServices;
 using BTCPayServer.Services.Stores;
 
 namespace BTCPayServer.Services.Mails
 {
     public class EmailSenderFactory
     {
-        private readonly IBackgroundJobClient _JobClient;
+        private readonly IBackgroundJobClient _jobClient;
-        private readonly SettingsRepository _Repository;
+        private readonly SettingsRepository _repository;
-        private readonly StoreRepository _StoreRepository;
+        private readonly StoreRepository _storeRepository;
+        private readonly CssThemeManager _cssThemeManager;
 
         public EmailSenderFactory(IBackgroundJobClient jobClient,
             SettingsRepository repository,
-            StoreRepository storeRepository)
+            StoreRepository storeRepository,
+            CssThemeManager cssThemeManager)
         {
-            _JobClient = jobClient;
+            _jobClient = jobClient;
-            _Repository = repository;
+            _repository = repository;
-            _StoreRepository = storeRepository;
+            _storeRepository = storeRepository;
+            _cssThemeManager = cssThemeManager;
         }
 
         public IEmailSender GetEmailSender(string storeId = null)
         {
-            var serverSender = new ServerEmailSender(_Repository, _JobClient);
+            var serverSender = new ServerEmailSender(_repository, _jobClient);
             if (string.IsNullOrEmpty(storeId))
                 return serverSender;
-            return new StoreEmailSender(_StoreRepository, serverSender, _JobClient, storeId);
+            return new StoreEmailSender(_storeRepository,
+                !_cssThemeManager.Policies.DisableStoresToUseServerEmailSettings ? serverSender : null, _jobClient,
+                storeId);
         }
     }
 }

BTCPayServer/Services/PoliciesSettings.cs

@@ -28,6 +28,10 @@ namespace BTCPayServer.Services
         public bool CheckForNewVersions { get; set; }        
         [Display(Name = "Disable notifications automatically showing (no websockets)")]
         public bool DisableInstantNotifications { get; set; }
+        [Display(Name = "Disable stores falling back to using the server's email settings")]
+        public bool DisableStoresToUseServerEmailSettings { get; set; }
+        [Display(Name = "Disable unauthenticated Create User API")]
+        public bool DisableUnauthenticatedUserApi { get; set; }
 
         [Display(Name = "Display app on website root")]
         public string RootAppId { get; set; }

BTCPayServer/Views/Server/Policies.cshtml

@@ -63,6 +63,16 @@
             <label asp-for="DisableInstantNotifications" class="form-check-label"></label>
             <span asp-validation-for="DisableInstantNotifications" class="text-danger"></span>
         </div>
+        <div class="form-check">
+            <input asp-for="DisableStoresToUseServerEmailSettings" type="checkbox" class="form-check-input"/>
+            <label asp-for="DisableStoresToUseServerEmailSettings" class="form-check-label"></label>
+            <span asp-validation-for="DisableStoresToUseServerEmailSettings" class="text-danger"></span>
+        </div>
+        <div class="form-check">
+            <input asp-for="DisableUnauthenticatedUserApi" type="checkbox" class="form-check-input"/>
+            <label asp-for="DisableUnauthenticatedUserApi" class="form-check-label"></label>
+            <span asp-validation-for="DisableUnauthenticatedUserApi" class="text-danger"></span>
+        </div>
         @if (ViewBag.UpdateUrlPresent)
         {
             <div class="form-check">