feat: Enhance OAuth client management to support platform_service usage and update related API scopes

docs/DESIGN.md

@@ -43,7 +43,7 @@
 - roles / user_roles (Identity)
   - id, name, created_at
 - OpenIddictApplications
-  - id, client_id, client_secret, display_name, permissions, redirect_uris, properties（含 `tenant_id`, `usage=tenant_api|webhook_outbound`）
+  - id, client_id, client_secret, display_name, permissions, redirect_uris, properties（含 `tenant_id`, `usage=tenant_api|webhook_outbound|platform_service`）
 - OpenIddictAuthorizations
   - id, application_id, status, subject, type, scopes
 - OpenIddictTokens
@@ -110,6 +110,9 @@
 4) 呼叫 Member Center API 將 email 加入 `email_blacklist`
 5) Member Center 對該 email 的訂閱事件全部忽略且不再推送
 6) 回寫請求需帶 `tenant_id + subscriber_id + list_id`，Member Center 端做租戶邊界驗證
+7) 回寫授權可用：
+   - tenant client scope：`newsletter:events.write`
+   - platform client scope：`newsletter:events.write.global`（SES 聚合事件）
 
 ### 6.5 註冊後銜接
 1) 使用者完成註冊
@@ -141,10 +144,11 @@
 - `POST /subscriptions/disable`：Send Engine → Member Center 黑名單回寫
 
 ### Auth / Scope
-- OAuth Client 綁定 `tenant_id`，所有清單/事件 API 需驗證租戶邊界
-- OAuth Client 需區分用途：`tenant_api` 與 `webhook_outbound`（禁止混用）
+- `tenant_api` / `webhook_outbound` OAuth Client 綁定 `tenant_id`，所有清單/事件 API 需驗證租戶邊界
+- OAuth Client 需區分用途：`tenant_api` / `webhook_outbound` / `platform_service`（禁止混用）
 - 新增 scope：`newsletter:list.read`、`newsletter:events.read`
 - 新增 scope：`newsletter:events.write`
+- 新增 scope：`newsletter:events.write.global`
 
 ### 租戶端取 Token（Client Credentials）
 - 租戶使用 OAuth Client Credentials 向 Member Center 取得 access token

docs/FLOWS.md

@@ -48,7 +48,10 @@
 - [API] Send Engine 依事件規則處理：
 - [API] `hard_bounce` / `soft_bounce_threshold` / `suppression`：設黑名單後回寫
 - [API] `complaint`：先在 Send Engine 取消訂閱，再回寫黑名單
-- [API] 呼叫 `POST /subscriptions/disable`（scope: `newsletter:events.write`），body 需含 `tenant_id + subscriber_id + list_id + reason + disabled_by + occurred_at`
+- [API] 呼叫 `POST /subscriptions/disable`：
+- [API] tenant client 用 `newsletter:events.write`
+- [API] 平台 client（SES 聚合事件）用 `newsletter:events.write.global`
+- [API] body 需含 `tenant_id + subscriber_id + list_id + reason + disabled_by + occurred_at`
 - [API] Member Center 將 email 寫入 `email_blacklist`，停用寄送並停止事件推送
 
 ## F-07 會員資料查看

docs/OPENAPI.md

@@ -63,13 +63,18 @@
 ## OAuth Client 用途分離（強制）
 - `usage=tenant_api`：
   - 供租戶站台拿 token 呼叫 Member Center / Send Engine API
-  - scope 僅給業務所需（如 `newsletter:send.write`、`newsletter:list.read`）
+  - scope 僅給業務所需（如 `newsletter:events.write`）
 - `usage=webhook_outbound`：
   - 供 Member Center 內部標記「對外 webhook 用」的租戶憑證用途
   - 不可用於租戶 API 呼叫
   - `X-Client-Id` 仍以 Send Engine `auth_clients.id` 為準
+- `usage=platform_service`：
+  - 供平台級 S2S（例如 SES 聚合事件回寫）
+  - 可不綁定 `tenant_id`，scope 使用 `newsletter:events.write.global`
+- `tenant_api` / `platform_service` 建議（且實作要求）`client_type=confidential`
 - 管理規則：
   - 每個 tenant 至少 2 組憑證（`tenant_api` / `webhook_outbound`）
+  - 平台級流程另建 `platform_service` 憑證
   - secret 分開輪替，禁止共用
 
 ## 整合 API / Auth（狀態）
@@ -80,13 +85,17 @@
 - `POST /subscriptions/disable`：已實作（Send Engine 回寫黑名單）
 
 ### Auth / Scope
-- OAuth Client 需綁定 `tenant_id`
+- `tenant_api` / `webhook_outbound` 類型需綁定 `tenant_id`
+- `platform_service` 可不綁定 `tenant_id`
 - 新增 scope：
   - `newsletter:list.read`
   - `newsletter:events.read`
   - `newsletter:events.write`
+  - `newsletter:events.write.global`
 - 發送引擎僅能用上述 scope，禁止 admin 權限
-- `POST /subscriptions/disable` 需 Bearer token 且包含 `newsletter:events.write`
+- `POST /subscriptions/disable` 需 Bearer token 且包含下列其一：
+  - `newsletter:events.write`（tenant-scoped）
+  - `newsletter:events.write.global`（platform-scoped，SES 回寫用）
 - 建議 Send Engine 使用 client credentials 取 token，不建議使用長效固定 token
 
 ### 回寫原因碼（Send Engine -> Member Center）

docs/UI.md

@@ -48,7 +48,7 @@
 
 ### 管理者端（統一 UI）
 - UC-11 租戶管理: `/admin/tenants`
-- UC-12 OAuth Client 管理: `/admin/oauth-clients`（建立時顯示一次 client_secret，可旋轉；需選 `usage=tenant_api` 或 `usage=webhook_outbound`）
+- UC-12 OAuth Client 管理: `/admin/oauth-clients`（建立時顯示一次 client_secret，可旋轉；可選 `usage=tenant_api` / `webhook_outbound` / `platform_service`；`platform_service` 可不指定 tenant）
 - UC-13 電子報清單管理: `/admin/newsletter-lists`
 - UC-14 訂閱查詢 / 匯出: `/admin/subscriptions`, `/admin/subscriptions/export`
 - UC-15 審計紀錄查詢: `/admin/audit-logs`

docs/openapi.yaml

@@ -440,7 +440,7 @@ paths:
     post:
       summary: Disable email (global blacklist)
       security: [{ BearerAuth: [] }]
-      description: Requires scope `newsletter:events.write`. Request must include `tenant_id`, `subscriber_id`, and `list_id` for tenant-boundary validation. Expected reason codes: `hard_bounce`, `soft_bounce_threshold`, `complaint`, `suppression`.
+      description: Requires scope `newsletter:events.write` (tenant client) or `newsletter:events.write.global` (platform client). Request must include `tenant_id`, `subscriber_id`, and `list_id` for tenant-boundary validation. Expected reason codes: `hard_bounce`, `soft_bounce_threshold`, `complaint`, `suppression`.
       requestBody:
         required: true
         content:
@@ -722,6 +722,10 @@ components:
             openid: OpenID Connect
             email: Email
             profile: Basic profile
+            newsletter:list.read: Read newsletter subscriptions by list
+            newsletter:events.read: Read newsletter events
+            newsletter:events.write: Write newsletter events (tenant scoped)
+            newsletter:events.write.global: Write newsletter events (platform scoped)
     BearerAuth:
       type: http
       scheme: bearer
@@ -907,8 +911,10 @@ components:
       type: object
       properties:
         id: { type: string }
-        tenant_id: { type: string }
+        tenant_id:
+          type: string
+          nullable: true
         name: { type: string }
-        usage: { type: string, enum: [tenant_api, webhook_outbound] }
+        usage: { type: string, enum: [tenant_api, webhook_outbound, platform_service] }
         redirect_uris: { type: array, items: { type: string } }
         client_type: { type: string, enum: [public, confidential] }

src/MemberCenter.Api/Contracts/AdminRequests.cs

@@ -4,4 +4,4 @@ public sealed record TenantRequest(string Name, List<string> Domains, string Sta
 
 public sealed record NewsletterListRequest(Guid TenantId, string Name, string Status);
 
-public sealed record OAuthClientRequest(Guid TenantId, string Name, List<string> RedirectUris, string ClientType);
+public sealed record OAuthClientRequest(Guid? TenantId, string Name, List<string> RedirectUris, string ClientType, string Usage = "tenant_api");

src/MemberCenter.Api/Controllers/AdminOAuthClientsController.cs

@@ -41,30 +41,40 @@ public class AdminOAuthClientsController : ControllerBase
     [HttpPost]
     public async Task<IActionResult> Create([FromBody] OAuthClientRequest request)
     {
+        if (!IsValidUsage(request.Usage))
+        {
+            return BadRequest("usage must be tenant_api, webhook_outbound, or platform_service.");
+        }
+
+        if (!IsTenantOptionalUsage(request.Usage) && (!request.TenantId.HasValue || request.TenantId.Value == Guid.Empty))
+        {
+            return BadRequest("tenant_id is required for this usage.");
+        }
+
+        if (RequiresClientCredentials(request.Usage)
+            && !string.Equals(request.ClientType, OpenIddictConstants.ClientTypes.Confidential, StringComparison.OrdinalIgnoreCase))
+        {
+            return BadRequest("client_type must be confidential for this usage.");
+        }
+
         var descriptor = new OpenIddictApplicationDescriptor
         {
             ClientId = Guid.NewGuid().ToString("N"),
             DisplayName = request.Name,
-            ClientType = request.ClientType,
-            Permissions =
-            {
-                OpenIddictConstants.Permissions.Endpoints.Authorization,
-                OpenIddictConstants.Permissions.Endpoints.Token,
-                OpenIddictConstants.Permissions.GrantTypes.AuthorizationCode,
-                OpenIddictConstants.Permissions.GrantTypes.RefreshToken,
-                OpenIddictConstants.Permissions.ResponseTypes.Code,
-                OpenIddictConstants.Permissions.Scopes.Email,
-                OpenIddictConstants.Permissions.Scopes.Profile,
-                "scp:openid"
-            }
+            ClientType = request.ClientType
         };
+        ApplyPermissions(descriptor, request.Usage);
 
         foreach (var uri in request.RedirectUris)
         {
             descriptor.RedirectUris.Add(new Uri(uri));
         }
 
-        descriptor.Properties["tenant_id"] = JsonSerializer.SerializeToElement(request.TenantId.ToString());
+        if (!IsTenantOptionalUsage(request.Usage) && request.TenantId.HasValue)
+        {
+            descriptor.Properties["tenant_id"] = JsonSerializer.SerializeToElement(request.TenantId.Value.ToString());
+        }
+        descriptor.Properties["usage"] = JsonSerializer.SerializeToElement(request.Usage);
 
         await _applicationManager.CreateAsync(descriptor);
 
@@ -100,6 +110,22 @@ public class AdminOAuthClientsController : ControllerBase
     [HttpPut("{id}")]
     public async Task<IActionResult> Update(string id, [FromBody] OAuthClientRequest request)
     {
+        if (!IsValidUsage(request.Usage))
+        {
+            return BadRequest("usage must be tenant_api, webhook_outbound, or platform_service.");
+        }
+
+        if (!IsTenantOptionalUsage(request.Usage) && (!request.TenantId.HasValue || request.TenantId.Value == Guid.Empty))
+        {
+            return BadRequest("tenant_id is required for this usage.");
+        }
+
+        if (RequiresClientCredentials(request.Usage)
+            && !string.Equals(request.ClientType, OpenIddictConstants.ClientTypes.Confidential, StringComparison.OrdinalIgnoreCase))
+        {
+            return BadRequest("client_type must be confidential for this usage.");
+        }
+
         var app = await _applicationManager.FindByIdAsync(id);
         if (app is null)
         {
@@ -111,12 +137,21 @@ public class AdminOAuthClientsController : ControllerBase
 
         descriptor.DisplayName = request.Name;
         descriptor.ClientType = request.ClientType;
+        ApplyPermissions(descriptor, request.Usage);
         descriptor.RedirectUris.Clear();
         foreach (var uri in request.RedirectUris)
         {
             descriptor.RedirectUris.Add(new Uri(uri));
         }
-        descriptor.Properties["tenant_id"] = JsonSerializer.SerializeToElement(request.TenantId.ToString());
+        if (!IsTenantOptionalUsage(request.Usage) && request.TenantId.HasValue)
+        {
+            descriptor.Properties["tenant_id"] = JsonSerializer.SerializeToElement(request.TenantId.Value.ToString());
+        }
+        else
+        {
+            descriptor.Properties.Remove("tenant_id");
+        }
+        descriptor.Properties["usage"] = JsonSerializer.SerializeToElement(request.Usage);
 
         await _applicationManager.UpdateAsync(app, descriptor);
 
@@ -141,4 +176,51 @@ public class AdminOAuthClientsController : ControllerBase
         await _applicationManager.DeleteAsync(app);
         return NoContent();
     }
+
+    private static bool IsValidUsage(string usage)
+    {
+        return string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "webhook_outbound", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase);
+    }
+
+    private static bool IsTenantOptionalUsage(string usage)
+    {
+        return string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase);
+    }
+
+    private static bool RequiresClientCredentials(string usage)
+    {
+        return string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase);
+    }
+
+    private static void ApplyPermissions(OpenIddictApplicationDescriptor descriptor, string usage)
+    {
+        descriptor.Permissions.Clear();
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.Endpoints.Token);
+
+        if (string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase))
+        {
+            descriptor.Permissions.Add(OpenIddictConstants.Permissions.GrantTypes.ClientCredentials);
+            if (string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase))
+            {
+                descriptor.Permissions.Add("scp:newsletter:events.write.global");
+            }
+            else
+            {
+                descriptor.Permissions.Add("scp:newsletter:events.write");
+            }
+            return;
+        }
+
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.Endpoints.Authorization);
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.GrantTypes.AuthorizationCode);
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.GrantTypes.RefreshToken);
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.ResponseTypes.Code);
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.Scopes.Email);
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.Scopes.Profile);
+        descriptor.Permissions.Add("scp:openid");
+    }
 }

src/MemberCenter.Api/Controllers/SubscriptionsController.cs

@@ -35,7 +35,9 @@ public class SubscriptionsController : ControllerBase
     [HttpPost("disable")]
     public async Task<IActionResult> Disable([FromBody] DisableSubscriptionRequest request)
     {
-        if (!HasScope(User, "newsletter:events.write"))
+        var hasTenantScope = HasScope(User, "newsletter:events.write");
+        var hasGlobalScope = HasScope(User, "newsletter:events.write.global");
+        if (!hasTenantScope && !hasGlobalScope)
         {
             return Forbid();
         }
@@ -54,6 +56,11 @@ public class SubscriptionsController : ControllerBase
             return BadRequest("reason must be one of: hard_bounce, soft_bounce_threshold, complaint, suppression.");
         }
 
+        if (!hasGlobalScope && TryGetTenantId(User, out var tokenTenantId) && tokenTenantId != request.TenantId)
+        {
+            return BadRequest("tenant_id does not match token tenant scope.");
+        }
+
         var target = await (
             from subscription in _dbContext.NewsletterSubscriptions
             join list in _dbContext.NewsletterLists on subscription.ListId equals list.Id
@@ -90,4 +97,11 @@ public class SubscriptionsController : ControllerBase
             .SelectMany(c => c.Value.Split(' ', StringSplitOptions.RemoveEmptyEntries));
         return values.Contains(scope, StringComparer.Ordinal);
     }
+
+    private static bool TryGetTenantId(System.Security.Claims.ClaimsPrincipal user, out Guid tenantId)
+    {
+        tenantId = Guid.Empty;
+        var value = user.FindFirst("tenant_id")?.Value;
+        return !string.IsNullOrWhiteSpace(value) && Guid.TryParse(value, out tenantId);
+    }
 }

src/MemberCenter.Api/Controllers/TokenController.cs

@@ -5,6 +5,8 @@ using Microsoft.AspNetCore.Identity;
 using Microsoft.AspNetCore.Mvc;
 using OpenIddict.Abstractions;
 using OpenIddict.Server.AspNetCore;
+using System.Security.Claims;
+using System.Text.Json;
 
 namespace MemberCenter.Api.Controllers;
 
@@ -13,11 +15,16 @@ public class TokenController : ControllerBase
 {
     private readonly UserManager<ApplicationUser> _userManager;
     private readonly SignInManager<ApplicationUser> _signInManager;
+    private readonly IOpenIddictApplicationManager _applicationManager;
 
-    public TokenController(UserManager<ApplicationUser> userManager, SignInManager<ApplicationUser> signInManager)
+    public TokenController(
+        UserManager<ApplicationUser> userManager,
+        SignInManager<ApplicationUser> signInManager,
+        IOpenIddictApplicationManager applicationManager)
     {
         _userManager = userManager;
         _signInManager = signInManager;
+        _applicationManager = applicationManager;
     }
 
     [HttpPost("/oauth/token")]
@@ -69,6 +76,61 @@ public class TokenController : ControllerBase
             return SignIn(principal, OpenIddictServerAspNetCoreDefaults.AuthenticationScheme);
         }
 
+        if (request.IsClientCredentialsGrantType())
+        {
+            if (string.IsNullOrWhiteSpace(request.ClientId))
+            {
+                return Forbid(OpenIddictServerAspNetCoreDefaults.AuthenticationScheme);
+            }
+
+            var app = await _applicationManager.FindByClientIdAsync(request.ClientId);
+            if (app is null)
+            {
+                return Forbid(OpenIddictServerAspNetCoreDefaults.AuthenticationScheme);
+            }
+
+            var identity = new ClaimsIdentity(
+                authenticationType: OpenIddictServerAspNetCoreDefaults.AuthenticationScheme,
+                nameType: OpenIddictConstants.Claims.Name,
+                roleType: OpenIddictConstants.Claims.Role);
+
+            identity.AddClaim(OpenIddictConstants.Claims.Subject, request.ClientId);
+            identity.AddClaim(OpenIddictConstants.Claims.ClientId, request.ClientId);
+
+            var properties = await _applicationManager.GetPropertiesAsync(app);
+            if (properties.TryGetValue("tenant_id", out var tenantValue))
+            {
+                var tenantId = tenantValue.ValueKind == JsonValueKind.String
+                    ? tenantValue.GetString()
+                    : tenantValue.ToString();
+                if (!string.IsNullOrWhiteSpace(tenantId))
+                {
+                    identity.AddClaim("tenant_id", tenantId);
+                }
+            }
+
+            if (properties.TryGetValue("usage", out var usageValue))
+            {
+                var usage = usageValue.ValueKind == JsonValueKind.String
+                    ? usageValue.GetString()
+                    : usageValue.ToString();
+                if (!string.IsNullOrWhiteSpace(usage))
+                {
+                    identity.AddClaim("client_usage", usage);
+                }
+            }
+
+            var principal = new ClaimsPrincipal(identity);
+            principal.SetScopes(request.Scope.GetScopesOrDefault());
+
+            foreach (var claim in principal.Claims)
+            {
+                claim.SetDestinations(ClaimsExtensions.GetDestinations(claim));
+            }
+
+            return SignIn(principal, OpenIddictServerAspNetCoreDefaults.AuthenticationScheme);
+        }
+
         return BadRequest("Unsupported grant type.");
     }
 }

src/MemberCenter.Api/Program.cs

@@ -56,13 +56,18 @@ builder.Services.AddOpenIddict()
             .RequireProofKeyForCodeExchange();
         options.AllowRefreshTokenFlow();
         options.AllowPasswordFlow();
+        options.AllowClientCredentialsFlow();
 
         options.AcceptAnonymousClients();
 
         options.RegisterScopes(
             OpenIddictConstants.Scopes.OpenId,
             OpenIddictConstants.Scopes.Email,
-            OpenIddictConstants.Scopes.Profile);
+            OpenIddictConstants.Scopes.Profile,
+            "newsletter:list.read",
+            "newsletter:events.read",
+            "newsletter:events.write",
+            "newsletter:events.write.global");
 
         options.AddDevelopmentEncryptionCertificate();
         options.AddDevelopmentSigningCertificate();

src/MemberCenter.Web/Controllers/Admin/OAuthClientsController.cs

@@ -61,7 +61,18 @@ public class OAuthClientsController : Controller
     {
         if (!IsValidUsage(model.Usage))
         {
-            ModelState.AddModelError(nameof(model.Usage), "Usage must be tenant_api or webhook_outbound.");
+            ModelState.AddModelError(nameof(model.Usage), "Usage must be tenant_api, webhook_outbound, or platform_service.");
+        }
+
+        if (!IsTenantOptionalUsage(model.Usage) && (!model.TenantId.HasValue || model.TenantId.Value == Guid.Empty))
+        {
+            ModelState.AddModelError(nameof(model.TenantId), "Tenant is required for this usage.");
+        }
+
+        if (RequiresClientCredentials(model.Usage)
+            && !string.Equals(model.ClientType, OpenIddictConstants.ClientTypes.Confidential, StringComparison.OrdinalIgnoreCase))
+        {
+            ModelState.AddModelError(nameof(model.ClientType), "Client type must be confidential for this usage.");
         }
 
         if (!ModelState.IsValid)
@@ -75,23 +86,7 @@ public class OAuthClientsController : Controller
             ? Convert.ToBase64String(System.Security.Cryptography.RandomNumberGenerator.GetBytes(32))
             : null;
 
-        var descriptor = new OpenIddictApplicationDescriptor
-        {
-            ClientId = clientId,
-            DisplayName = model.Name,
-            ClientType = model.ClientType,
-            Permissions =
-            {
-                OpenIddictConstants.Permissions.Endpoints.Authorization,
-                OpenIddictConstants.Permissions.Endpoints.Token,
-                OpenIddictConstants.Permissions.GrantTypes.AuthorizationCode,
-                OpenIddictConstants.Permissions.GrantTypes.RefreshToken,
-                OpenIddictConstants.Permissions.ResponseTypes.Code,
-                OpenIddictConstants.Permissions.Scopes.Email,
-                OpenIddictConstants.Permissions.Scopes.Profile,
-                "scp:openid"
-            }
-        };
+        var descriptor = BuildDescriptor(clientId, model.Name, model.ClientType, model.Usage);
         if (!string.IsNullOrWhiteSpace(clientSecret))
         {
             descriptor.ClientSecret = clientSecret;
@@ -102,7 +97,10 @@ public class OAuthClientsController : Controller
             descriptor.RedirectUris.Add(new Uri(uri));
         }
 
-        descriptor.Properties["tenant_id"] = System.Text.Json.JsonSerializer.SerializeToElement(model.TenantId.ToString());
+        if (!IsTenantOptionalUsage(model.Usage) && model.TenantId.HasValue)
+        {
+            descriptor.Properties["tenant_id"] = System.Text.Json.JsonSerializer.SerializeToElement(model.TenantId.Value.ToString());
+        }
         descriptor.Properties["usage"] = System.Text.Json.JsonSerializer.SerializeToElement(model.Usage);
 
         await _applicationManager.CreateAsync(descriptor);
@@ -134,7 +132,7 @@ public class OAuthClientsController : Controller
 
         return View(new OAuthClientFormViewModel
         {
-            TenantId = Guid.TryParse(tenantId, out var parsed) ? parsed : Guid.Empty,
+            TenantId = Guid.TryParse(tenantId, out var parsed) ? parsed : null,
             Name = await _applicationManager.GetDisplayNameAsync(app) ?? string.Empty,
             ClientType = await _applicationManager.GetClientTypeAsync(app) ?? "public",
             Usage = string.IsNullOrWhiteSpace(usage) ? "tenant_api" : usage,
@@ -148,7 +146,18 @@ public class OAuthClientsController : Controller
     {
         if (!IsValidUsage(model.Usage))
         {
-            ModelState.AddModelError(nameof(model.Usage), "Usage must be tenant_api or webhook_outbound.");
+            ModelState.AddModelError(nameof(model.Usage), "Usage must be tenant_api, webhook_outbound, or platform_service.");
+        }
+
+        if (!IsTenantOptionalUsage(model.Usage) && (!model.TenantId.HasValue || model.TenantId.Value == Guid.Empty))
+        {
+            ModelState.AddModelError(nameof(model.TenantId), "Tenant is required for this usage.");
+        }
+
+        if (RequiresClientCredentials(model.Usage)
+            && !string.Equals(model.ClientType, OpenIddictConstants.ClientTypes.Confidential, StringComparison.OrdinalIgnoreCase))
+        {
+            ModelState.AddModelError(nameof(model.ClientType), "Client type must be confidential for this usage.");
         }
 
         if (!ModelState.IsValid)
@@ -168,12 +177,20 @@ public class OAuthClientsController : Controller
 
         descriptor.DisplayName = model.Name;
         descriptor.ClientType = model.ClientType;
+        ApplyPermissions(descriptor, model.Usage);
         descriptor.RedirectUris.Clear();
         foreach (var uri in model.RedirectUris.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries))
         {
             descriptor.RedirectUris.Add(new Uri(uri));
         }
-        descriptor.Properties["tenant_id"] = System.Text.Json.JsonSerializer.SerializeToElement(model.TenantId.ToString());
+        if (!IsTenantOptionalUsage(model.Usage) && model.TenantId.HasValue)
+        {
+            descriptor.Properties["tenant_id"] = System.Text.Json.JsonSerializer.SerializeToElement(model.TenantId.Value.ToString());
+        }
+        else
+        {
+            descriptor.Properties.Remove("tenant_id");
+        }
         descriptor.Properties["usage"] = System.Text.Json.JsonSerializer.SerializeToElement(model.Usage);
 
         await _applicationManager.UpdateAsync(app, descriptor);
@@ -225,6 +242,60 @@ public class OAuthClientsController : Controller
     private static bool IsValidUsage(string usage)
     {
         return string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase)
-            || string.Equals(usage, "webhook_outbound", StringComparison.OrdinalIgnoreCase);
+            || string.Equals(usage, "webhook_outbound", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase);
+    }
+
+    private static bool IsTenantOptionalUsage(string usage)
+    {
+        return string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase);
+    }
+
+    private static bool RequiresClientCredentials(string usage)
+    {
+        return string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase);
+    }
+
+    private static OpenIddictApplicationDescriptor BuildDescriptor(string clientId, string name, string clientType, string usage)
+    {
+        var descriptor = new OpenIddictApplicationDescriptor
+        {
+            ClientId = clientId,
+            DisplayName = name,
+            ClientType = clientType
+        };
+
+        ApplyPermissions(descriptor, usage);
+        return descriptor;
+    }
+
+    private static void ApplyPermissions(OpenIddictApplicationDescriptor descriptor, string usage)
+    {
+        descriptor.Permissions.Clear();
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.Endpoints.Token);
+
+        if (string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase))
+        {
+            descriptor.Permissions.Add(OpenIddictConstants.Permissions.GrantTypes.ClientCredentials);
+            if (string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase))
+            {
+                descriptor.Permissions.Add("scp:newsletter:events.write.global");
+            }
+            else
+            {
+                descriptor.Permissions.Add("scp:newsletter:events.write");
+            }
+            return;
+        }
+
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.Endpoints.Authorization);
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.GrantTypes.AuthorizationCode);
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.GrantTypes.RefreshToken);
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.ResponseTypes.Code);
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.Scopes.Email);
+        descriptor.Permissions.Add(OpenIddictConstants.Permissions.Scopes.Profile);
+        descriptor.Permissions.Add("scp:openid");
     }
 }

src/MemberCenter.Web/Models/Admin/OAuthClientFormViewModel.cs

@@ -4,8 +4,7 @@ namespace MemberCenter.Web.Models.Admin;
 
 public sealed class OAuthClientFormViewModel
 {
-    [Required]
-    public Guid TenantId { get; set; }
+    public Guid? TenantId { get; set; }
 
     [Required]
     public string Name { get; set; } = string.Empty;

src/MemberCenter.Web/Views/Admin/OAuthClients/Create.cshtml

@@ -27,6 +27,7 @@
   <select asp-for="Usage">
     <option value="tenant_api">tenant_api</option>
     <option value="webhook_outbound">webhook_outbound</option>
+    <option value="platform_service">platform_service</option>
   </select>
   <span asp-validation-for="Usage"></span>
 

src/MemberCenter.Web/Views/Admin/OAuthClients/Edit.cshtml

@@ -27,6 +27,7 @@
   <select asp-for="Usage">
     <option value="tenant_api">tenant_api</option>
     <option value="webhook_outbound">webhook_outbound</option>
+    <option value="platform_service">platform_service</option>
   </select>
   <span asp-validation-for="Usage"></span>