feat: Enhance OAuth client management and add one-click unsubscribe functionality

- Updated OpenAPI documentation to include new OAuth2 usage types: `send_api`.
- Added endpoints for issuing one-click unsubscribe tokens in both single and batch requests.
- Modified OAuth client creation and management to enforce new usage types and redirect URI requirements.
- Implemented logic in the Newsletter service to handle one-click unsubscribe token issuance.
- Updated UI to reflect changes in OAuth client usage options and redirect URI handling.
- Enhanced token generation logic to support new scopes and audience settings for Send Engine.

.env.example

@@ -1,5 +1,8 @@
 ASPNETCORE_ENVIRONMENT=Development
 ConnectionStrings__Default=Host=localhost;Database=member_center;Username=postgres;Password=postgres
+Auth__Issuer=http://localhost:7850/
+Auth__MemberCenterAudience=member_center_api
+Auth__SendEngineAudience=send_engine_api
 SendEngine__BaseUrl=http://localhost:6060
 SendEngine__WebhookSecret=change-me
 Testing__DisableSubscriptionDryRunNoDb=false

README.md

@@ -41,7 +41,6 @@
 - `docs/openapi.yaml`：OpenAPI 3.1 正式規格檔
 - `docs/SCHEMA.sql`：資料庫 schema（PostgreSQL）
 - `docs/SEED.sql`：初始化/測試資料
-- `docs/SEND_ENGINE.md`：自建發送引擎摘要（規劃）
 - `docs/MESSMAIL.md`：租戶站台介接指引（訂閱/退訂/發信）
 - `docs/TECH_STACK.md`：技術棧與選型
 - `docs/INSTALL.md`：安裝、初始化與維運指令

docs/DESIGN.md

@@ -16,7 +16,7 @@
 - 各站自行設計 UI，主要走 API；少數狀況使用 redirect
 - 多租戶為邏輯隔離，但會員資料跨站共享
 - 公開訂閱端點必須使用 `list_id + email` 做資料邊界，禁止僅以 `email` 查詢或操作
-- 訂閱狀態同步採 event/queue
+- 訂閱狀態同步目前採 webhook（event payload）；queue 為後續可選擴充
 - PostgreSQL
 - 實作：C# .NET Core + MVC + OpenIddict
 
@@ -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|platform_service`）
+  - id, client_id, client_secret, display_name, permissions, redirect_uris, properties（含 `tenant_id`, `usage=tenant_api|send_api|webhook_outbound|platform_service`）
 - OpenIddictAuthorizations
   - id, application_id, status, subject, type, scopes
 - OpenIddictTokens
@@ -97,6 +97,12 @@
 2) 驗證 token 後將該訂閱標記為 `unsubscribed`
 3) 會員中心發出事件 `subscription.unsubscribed` 到 event/queue
 
+### 6.4b Send Engine 發信前申請 One-Click Token
+1) Send Engine 依收件者呼叫 `POST /newsletter/one-click-unsubscribe-token`，或批次呼叫 `POST /newsletter/one-click-unsubscribe-tokens`
+2) body 帶 `tenant_id + list_id + subscriber_id`（批次版為 `subscriber_ids[]`）
+3) 會員中心簽發 token（與手動退訂 token 分離 purpose）
+4) Send Engine 將 token 寫入 `List-Unsubscribe` 連結
+
 ### 6.6 Send Engine 事件同步（Member Center → Send Engine）
 1) Member Center 發出事件（`subscription.activated` / `subscription.unsubscribed` / `preferences.updated`）
 2) 以 webhook 推送至 Send Engine（簽章與重放防護）
@@ -130,6 +136,8 @@
 - GET `/newsletter/confirm`
 - POST `/newsletter/unsubscribe`
 - POST `/newsletter/unsubscribe-token`
+- POST `/newsletter/one-click-unsubscribe-token`
+- POST `/newsletter/one-click-unsubscribe-tokens`
 - GET `/newsletter/preferences`
 - POST `/newsletter/preferences`
 - POST `/webhooks/subscriptions`（Send Engine 端點，Member Center 呼叫）
@@ -137,24 +145,26 @@
 - POST `/subscriptions/disable`（Member Center 端點，Send Engine 呼叫）
 - POST `/integrations/send-engine/webhook-clients/upsert`（Member Center 端點，Send Engine 呼叫）
 
-## 7.1 待新增 API / Auth（規劃中）
+## 7.1 進度狀態（2026-02）
 ### API
-- `GET /newsletter/subscriptions?list_id=...`：供發送引擎同步訂閱清單
+- `GET /newsletter/subscriptions?list_id=...`：已實作
-- `POST /webhooks/subscriptions`：Member Center → Send Engine 事件推送
+- `POST /webhooks/subscriptions`：已實作（Member Center 發送）
-- `POST /webhooks/lists/full-sync`：Member Center → Send Engine 全量同步
+- `POST /subscriptions/disable`：已實作
-- `POST /subscriptions/disable`：Send Engine → Member Center 黑名單回寫
+- `POST /integrations/send-engine/webhook-clients/upsert`：已實作
+- `POST /webhooks/lists/full-sync`：尚未實作（保留規格）
 
 ### Auth / Scope
-- `tenant_api` / `webhook_outbound` OAuth Client 綁定 `tenant_id`，所有清單/事件 API 需驗證租戶邊界
+- `tenant_api` / `send_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）
+- OAuth Client 需區分用途：`tenant_api` / `send_api` / `webhook_outbound` / `platform_service`（禁止混用）
-- 新增 scope：`newsletter:list.read`、`newsletter:events.read`
+- 新增 scope：`newsletter:list.read`、`newsletter:send.write`、`newsletter:send.read`、`newsletter:events.read`
 - 新增 scope：`newsletter:events.write`
 - 新增 scope：`newsletter:events.write.global`
+- JWT Access Token 已改為 JWS（`DisableAccessTokenEncryption`），供 Send Engine 以 JWKS 驗簽
 
 ### 租戶端取 Token（Client Credentials）
 - 租戶使用 OAuth Client Credentials 向 Member Center 取得 access token
 - token 內含 `tenant_id` 與 scope
-- Send Engine 收到租戶請求後以 JWKS 驗簽（建議）或向 Member Center 進行 introspection
+- Send Engine 收到租戶請求後以 JWKS 驗簽 JWT（JWS）
 - 驗簽通過後將 `tenant_id` 固定在 request context，不接受 body 覆寫
 
 ## 8. 安全與合規

docs/FLOWS.md

@@ -3,7 +3,7 @@
 流程以「API 自建 UI」與「會員中心統一 UI」兩種模式描述。
 
 ## F-01 註冊會員
-- [API] 站點送出 `POST /auth/register`（待補 API）
+- [API] 站點送出 `POST /auth/register`
 - [API] 會員中心建立 user、寄送驗證信
 - [UI] 導向會員中心註冊頁完成註冊
 - [UI] 會員中心寄送驗證信
@@ -14,6 +14,12 @@
 - [UI] 導向 `/oauth/authorize` 完成授權碼流程
 - [UI] 站點用 code 換 token + id_token
 
+## F-02b 內容站台呼叫 Send Engine（Client Credentials + JWT 驗簽）
+- [API] 內容站台以 `client_credentials` 呼叫 `POST /oauth/token` 取得 access_token（`usage=send_api`）
+- [API] 內容站台帶 Bearer token 呼叫 Send Engine 建立發送任務
+- [API] Send Engine 以 Member Center JWKS 驗簽 token
+- [API] 驗證 `scope/tenant_id/exp` 通過後才受理任務
+
 ## F-03 忘記密碼 / 重設密碼
 - [API] 站點送出 `POST /auth/password/forgot`
 - [UI] 會員中心頁提交 email 並發送重設信
@@ -31,6 +37,12 @@
 - [UI] 訂閱狀態改為 unsubscribed
 - [API] 發出 event `subscription.unsubscribed`
 
+## F-05b One-Click 退訂 Token（Send Engine 發信前）
+- [API] Send Engine 以 `tenant_id + list_id + subscriber_id` 呼叫 `POST /newsletter/one-click-unsubscribe-token`
+- [API] 或以 `tenant_id + list_id + subscriber_ids[]` 呼叫 `POST /newsletter/one-click-unsubscribe-tokens` 批次取得
+- [API] Member Center 回傳 one-click `unsubscribe_token`
+- [API] Send Engine 將 token 置入信件 `List-Unsubscribe` URL
+
 ## F-06 訂閱偏好管理（登入後）
 - [API] 站點以 `list_id + email` 讀取 `/newsletter/preferences`
 - [API] 站點以 `list_id + email` 更新 `/newsletter/preferences`

docs/INSTALL.md

@@ -40,6 +40,9 @@
 ```
 ASPNETCORE_ENVIRONMENT=Development
 ConnectionStrings__Default=Host=localhost;Database=member_center;Username=postgres;Password=postgres
+Auth__Issuer=http://localhost:7850/
+Auth__MemberCenterAudience=member_center_api
+Auth__SendEngineAudience=send_engine_api
 SendEngine__BaseUrl=http://localhost:6060
 SendEngine__WebhookSecret=change-me
 ```

docs/MESSMAIL.md

@@ -53,7 +53,7 @@ End User
 租戶站台沒有真人帳號，使用 **Client Credentials** 取得 access token。
 
 - 向 Member Center 申請 OAuth Client
-- OAuth Client 必須使用 `usage=tenant_api`（不可使用 `webhook_outbound`）
+- OAuth Client 建議使用 `usage=send_api`（專供發送）；`tenant_api` 留給其他租戶 API
 - scope 依用途最小化
 
 建議 scopes：
@@ -77,6 +77,12 @@ curl -s -X POST https://{send-engine}/api/send-jobs \
   -d '{ \"tenant_id\": \"<TENANT_ID>\", \"list_id\": \"<LIST_ID>\", \"subject\": \"Weekly\", \"body_text\": \"Hello\" }'
 ```
 
+### Send Engine 驗證 Token（JWT / JWKS）
+- Send Engine 以 Member Center 的 JWKS 驗簽 access token（JWS）。
+- 驗證重點：`iss`、`aud`、`scope`、`tenant_id`、`exp`。
+- `iss`：由 Member Center `Auth__Issuer` 設定（例：`http://localhost:7850/`）
+- `aud`：Send Engine 流程預設 `send_engine_api`（可用 `Auth__SendEngineAudience` 覆寫）
+
 ---
 
 ## 3. API 表格（租戶站台 → Member Center）
@@ -90,6 +96,8 @@ curl -s -X POST https://{send-engine}/api/send-jobs \
 | 讀取偏好 | GET | `/newsletter/preferences` | `list_id`, `email` | 需 list_id + email |
 | 更新偏好 | POST | `/newsletter/preferences` | `list_id`, `email`, `preferences` | 需 list_id + email |
 
+---
+
 ### 訂閱（範例）
 ```bash
 curl -s -X POST https://{member-center}/newsletter/subscribe \

docs/OPENAPI.md

@@ -14,14 +14,17 @@
 - Admin：Tenants/Lists/OAuth Clients（MVP CRUD）
 
 ## Security Schemes
-- OAuth2 (Authorization Code + PKCE)
+- OAuth2 (Authorization Code + PKCE、Client Credentials)
 - Bearer JWT（API 使用）
 
 ## 補充說明
 - `/oauth/token`、`/auth/login`、`/auth/refresh` 使用 `application/x-www-form-urlencoded`
+- Access token 以 JWT（JWS）簽發，建議驗證 `iss` 與 `aud`
 - `/auth/email/verify` 需要 `token` + `email`
 - `/newsletter/subscribe` 會回傳 `confirm_token`
 - `/newsletter/unsubscribe-token` 需要 `list_id + email` 才能申請 `unsubscribe_token`
+- `/newsletter/one-click-unsubscribe-token` 提供 Send Engine 發信前取得 one-click 退訂 token（`tenant_id + list_id + subscriber_id`）
+- `/newsletter/one-click-unsubscribe-tokens` 提供 Send Engine 批次取得 one-click 退訂 token（`tenant_id + list_id + subscriber_ids[]`）
 - `/newsletter/preferences`（GET/POST）需要 `list_id + email`，避免跨租戶資料讀取/更新
 
 ## 通用欄位
@@ -65,14 +68,19 @@
 - `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:events.write`）
+- `usage=send_api`：
+  - 供租戶站台呼叫 Send Engine 發信流程
+  - 內建 scope：`newsletter:send.write`、`newsletter:send.read`
 - `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
+  - 需設定 `redirect_uris`（Authorization Code 流程）
 - `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`
+- `tenant_api` / `send_api` / `platform_service` 建議（且實作要求）`client_type=confidential`
+- `redirect_uris` 僅 `webhook_outbound` 需要；其他 usage 可為空
 - 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
@@ -85,12 +93,16 @@
 - `POST /webhooks/lists/full-sync`：規格已定義（Member Center 發送；Send Engine 接收）
 - `POST /subscriptions/disable`：已實作（Send Engine 回寫黑名單）
 - `POST /integrations/send-engine/webhook-clients/upsert`：已實作（Send Engine 回填 tenant webhook client id）
+- `POST /newsletter/one-click-unsubscribe-token`：已實作（Send Engine 發信前申請 one-click token）
+- `POST /newsletter/one-click-unsubscribe-tokens`：已實作（Send Engine 批次申請 one-click token）
 
 ### Auth / Scope
-- `tenant_api` / `webhook_outbound` 類型需綁定 `tenant_id`
+- `tenant_api` / `send_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:send.write`
+  - `newsletter:send.read`
   - `newsletter:events.read`
   - `newsletter:events.write`
   - `newsletter:events.write.global`
@@ -99,6 +111,11 @@
   - `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
+- Send Engine 建議以 JWKS 驗簽 JWT（JWS），並驗證 `scope/tenant_id/exp`
+  - `iss` 由 `Auth:Issuer` 設定（例：`http://localhost:7850/`）
+  - `aud` 預設：
+    - Send Engine 流程：`send_engine_api`（可用 `Auth:SendEngineAudience` 覆寫）
+    - Member Center API 流程：`member_center_api`（可用 `Auth:MemberCenterAudience` 覆寫）
 
 ### 回寫原因碼（Send Engine -> Member Center）
 - `hard_bounce`
@@ -115,3 +132,46 @@
 - `occurred_at`（RFC3339）
 
 Member Center 會用 `subscriber_id + list_id` 查詢訂閱，再驗證 `tenant_id` 邊界；驗證通過後才寫入全域 email 黑名單。
+
+### One-Click 退訂 Token 介接方式（Send Engine）
+用途：Send Engine 在寄信前批次向 Member Center 取得每位收件者的 one-click 退訂 token。
+
+步驟：
+1. 以 client credentials 取得 access token（scope：`newsletter:events.write` 或 `newsletter:events.write.global`）
+2. 呼叫 `POST /newsletter/one-click-unsubscribe-tokens`
+3. 將回傳 `status=issued` 的 `unsubscribe_token` 寫入每封信的 `List-Unsubscribe` URL
+
+Request（批次）：
+```json
+{
+  "tenant_id": "c9034414-43d6-404e-8d41-e80922420bf1",
+  "list_id": "a92fdeda-29bb-42ca-9c05-e7df3983288a",
+  "subscriber_ids": [
+    "33333333-3333-3333-3333-333333333333",
+    "44444444-4444-4444-4444-444444444444"
+  ]
+}
+```
+
+Response（批次）：
+```json
+{
+  "items": [
+    {
+      "subscriber_id": "33333333-3333-3333-3333-333333333333",
+      "unsubscribe_token": "token-xxx",
+      "status": "issued"
+    },
+    {
+      "subscriber_id": "44444444-4444-4444-4444-444444444444",
+      "unsubscribe_token": null,
+      "status": "blacklisted"
+    }
+  ]
+}
+```
+
+狀態說明：
+- `issued`：可直接用於 one-click 退訂連結
+- `not_found`：找不到對應訂閱者（tenant/list/subscriber 邊界不匹配）
+- `blacklisted`：已在黑名單，不提供 token

docs/UI.md

@@ -11,7 +11,7 @@
 
 ### 管理者端
 - 租戶管理（Tenant CRUD）
-- OAuth Client 管理（usage / redirect_uris / scopes / client_id / client_secret）
+- OAuth Client 管理（usage / redirect_uris / client_id / client_secret；scope 由 usage 自動配置）
 - 電子報清單管理（Lists CRUD）
 - 訂閱查詢 / 匯出
 - 審計紀錄查詢
@@ -49,7 +49,9 @@
 ### 管理者端（統一 UI）
 - UC-11 租戶管理: `/admin/tenants`
 - UC-11.1 Tenant 可設定 `Send Engine Webhook Client Id`（UUID）
-- 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-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` / `send_api` / `webhook_outbound` / `platform_service`；`platform_service` 可不指定 tenant）
+  - `redirect_uris` 僅 `webhook_outbound` 需要；其餘 usage 不需要
+  - `tenant_api` / `send_api` / `platform_service` 強制 `client_type=confidential`
 - 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

@@ -4,7 +4,7 @@ info:
   version: 0.1.0
   description: OAuth2/OIDC + Newsletter Subscription API
 servers:
-  - url: /api
+  - url: /
 security:
   - BearerAuth: []
 
@@ -59,6 +59,7 @@ paths:
               oneOf:
                 - $ref: '#/components/schemas/AuthorizationCodeTokenRequest'
                 - $ref: '#/components/schemas/RefreshTokenRequest'
+                - $ref: '#/components/schemas/ClientCredentialsTokenRequest'
       responses:
         '200':
           description: Token response
@@ -74,7 +75,7 @@ paths:
         '200':
           description: OIDC discovery document
 
-  /.well-known/jwks.json:
+  /.well-known/jwks:
     get:
       summary: JWKS
       responses:
@@ -339,6 +340,77 @@ paths:
               schema:
                 $ref: '#/components/schemas/ErrorResponse'
 
+  /newsletter/one-click-unsubscribe-token:
+    post:
+      summary: Issue one-click unsubscribe token (Send Engine pre-send)
+      security: [{ BearerAuth: [] }]
+      description: Requires scope `newsletter:events.write` or `newsletter:events.write.global`.
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/IssueOneClickUnsubscribeTokenRequest'
+      responses:
+        '200':
+          description: Unsubscribe token issued
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  unsubscribe_token: { type: string }
+        '400':
+          description: Bad request
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/ErrorResponse'
+        '401':
+          description: Unauthorized
+        '403':
+          description: Forbidden
+        '404':
+          description: Not found
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/ErrorResponse'
+
+  /newsletter/one-click-unsubscribe-tokens:
+    post:
+      summary: Issue one-click unsubscribe tokens in batch (Send Engine pre-send)
+      security: [{ BearerAuth: [] }]
+      description: Requires scope `newsletter:events.write` or `newsletter:events.write.global`.
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/IssueOneClickUnsubscribeTokensRequest'
+      responses:
+        '200':
+          description: Unsubscribe tokens issued
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  items:
+                    type: array
+                    items:
+                      $ref: '#/components/schemas/OneClickUnsubscribeTokenItem'
+        '400':
+          description: Bad request
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/ErrorResponse'
+        '401':
+          description: Unauthorized
+        '403':
+          description: Forbidden
+
   /newsletter/preferences:
     get:
       summary: Get preferences
@@ -739,13 +811,24 @@ components:
       type: oauth2
       flows:
         authorizationCode:
-          authorizationUrl: /api/oauth/authorize
+          authorizationUrl: /oauth/authorize
-          tokenUrl: /api/oauth/token
+          tokenUrl: /oauth/token
           scopes:
             openid: OpenID Connect
             email: Email
             profile: Basic profile
             newsletter:list.read: Read newsletter subscriptions by list
+            newsletter:send.write: Create/send newsletter jobs
+            newsletter:send.read: Read newsletter send status
+            newsletter:events.read: Read newsletter events
+            newsletter:events.write: Write newsletter events (tenant scoped)
+            newsletter:events.write.global: Write newsletter events (platform scoped)
+        clientCredentials:
+          tokenUrl: /oauth/token
+          scopes:
+            newsletter:list.read: Read newsletter subscriptions by list
+            newsletter:send.write: Create/send newsletter jobs
+            newsletter:send.read: Read newsletter send status
             newsletter:events.read: Read newsletter events
             newsletter:events.write: Write newsletter events (tenant scoped)
             newsletter:events.write.global: Write newsletter events (platform scoped)
@@ -806,6 +889,15 @@ components:
         refresh_token: { type: string }
         client_id: { type: string }
 
+    ClientCredentialsTokenRequest:
+      type: object
+      required: [grant_type, client_id, client_secret]
+      properties:
+        grant_type: { type: string, enum: [client_credentials] }
+        client_id: { type: string }
+        client_secret: { type: string }
+        scope: { type: string }
+
     ForgotPasswordRequest:
       type: object
       required: [email]
@@ -867,6 +959,31 @@ components:
         disabled_by: { type: string }
         occurred_at: { type: string, format: date-time }
 
+    IssueOneClickUnsubscribeTokenRequest:
+      type: object
+      required: [tenant_id, list_id, subscriber_id]
+      properties:
+        tenant_id: { type: string, format: uuid }
+        list_id: { type: string, format: uuid }
+        subscriber_id: { type: string, format: uuid }
+
+    IssueOneClickUnsubscribeTokensRequest:
+      type: object
+      required: [tenant_id, list_id, subscriber_ids]
+      properties:
+        tenant_id: { type: string, format: uuid }
+        list_id: { type: string, format: uuid }
+        subscriber_ids:
+          type: array
+          items: { type: string, format: uuid }
+
+    OneClickUnsubscribeTokenItem:
+      type: object
+      properties:
+        subscriber_id: { type: string, format: uuid }
+        unsubscribe_token: { type: string, nullable: true }
+        status: { type: string, enum: [issued, not_found, blacklisted] }
+
     ErrorResponse:
       type: object
       required: [error, message, request_id]
@@ -949,6 +1066,6 @@ components:
           type: string
           nullable: true
         name: { type: string }
-        usage: { type: string, enum: [tenant_api, webhook_outbound, platform_service] }
+        usage: { type: string, enum: [tenant_api, send_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, string Usage = "tenant_api");
+public sealed record OAuthClientRequest(Guid? TenantId, string Name, List<string>? RedirectUris, string ClientType, string Usage = "tenant_api");

src/MemberCenter.Api/Contracts/NewsletterRequests.cs

@@ -15,6 +15,16 @@ public sealed record IssueUnsubscribeTokenRequest(
     [property: JsonPropertyName("list_id")] Guid ListId,
     [property: JsonPropertyName("email")] string Email);
 
+public sealed record IssueOneClickUnsubscribeTokenRequest(
+    [property: JsonPropertyName("tenant_id")] Guid TenantId,
+    [property: JsonPropertyName("list_id")] Guid ListId,
+    [property: JsonPropertyName("subscriber_id")] Guid SubscriberId);
+
+public sealed record IssueOneClickUnsubscribeTokensRequest(
+    [property: JsonPropertyName("tenant_id")] Guid TenantId,
+    [property: JsonPropertyName("list_id")] Guid ListId,
+    [property: JsonPropertyName("subscriber_ids")] List<Guid> SubscriberIds);
+
 public sealed record UpdatePreferencesRequest(
     [property: JsonPropertyName("list_id")] Guid ListId,
     [property: JsonPropertyName("email")] string Email,

src/MemberCenter.Api/Controllers/AdminOAuthClientsController.cs

@@ -43,7 +43,7 @@ public class AdminOAuthClientsController : ControllerBase
     {
         if (!IsValidUsage(request.Usage))
         {
-            return BadRequest("usage must be tenant_api, webhook_outbound, or platform_service.");
+            return BadRequest("usage must be tenant_api, send_api, webhook_outbound, or platform_service.");
         }
 
         if (!IsTenantOptionalUsage(request.Usage) && (!request.TenantId.HasValue || request.TenantId.Value == Guid.Empty))
@@ -57,6 +57,16 @@ public class AdminOAuthClientsController : ControllerBase
             return BadRequest("client_type must be confidential for this usage.");
         }
 
+        var (redirectUris, redirectUriError) = NormalizeRedirectUris(request.RedirectUris);
+        if (!string.IsNullOrWhiteSpace(redirectUriError))
+        {
+            return BadRequest(redirectUriError);
+        }
+        if (UsesAuthorizationCodeFlow(request.Usage) && redirectUris.Count == 0)
+        {
+            return BadRequest("redirect_uris is required for webhook_outbound usage.");
+        }
+
         var descriptor = new OpenIddictApplicationDescriptor
         {
             ClientId = Guid.NewGuid().ToString("N"),
@@ -65,7 +75,7 @@ public class AdminOAuthClientsController : ControllerBase
         };
         ApplyPermissions(descriptor, request.Usage);
 
-        foreach (var uri in request.RedirectUris)
+        foreach (var uri in redirectUris)
         {
             descriptor.RedirectUris.Add(new Uri(uri));
         }
@@ -112,7 +122,7 @@ public class AdminOAuthClientsController : ControllerBase
     {
         if (!IsValidUsage(request.Usage))
         {
-            return BadRequest("usage must be tenant_api, webhook_outbound, or platform_service.");
+            return BadRequest("usage must be tenant_api, send_api, webhook_outbound, or platform_service.");
         }
 
         if (!IsTenantOptionalUsage(request.Usage) && (!request.TenantId.HasValue || request.TenantId.Value == Guid.Empty))
@@ -126,6 +136,16 @@ public class AdminOAuthClientsController : ControllerBase
             return BadRequest("client_type must be confidential for this usage.");
         }
 
+        var (redirectUris, redirectUriError) = NormalizeRedirectUris(request.RedirectUris);
+        if (!string.IsNullOrWhiteSpace(redirectUriError))
+        {
+            return BadRequest(redirectUriError);
+        }
+        if (UsesAuthorizationCodeFlow(request.Usage) && redirectUris.Count == 0)
+        {
+            return BadRequest("redirect_uris is required for webhook_outbound usage.");
+        }
+
         var app = await _applicationManager.FindByIdAsync(id);
         if (app is null)
         {
@@ -139,7 +159,7 @@ public class AdminOAuthClientsController : ControllerBase
         descriptor.ClientType = request.ClientType;
         ApplyPermissions(descriptor, request.Usage);
         descriptor.RedirectUris.Clear();
-        foreach (var uri in request.RedirectUris)
+        foreach (var uri in redirectUris)
         {
             descriptor.RedirectUris.Add(new Uri(uri));
         }
@@ -180,6 +200,7 @@ public class AdminOAuthClientsController : ControllerBase
     private static bool IsValidUsage(string usage)
     {
         return string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "send_api", StringComparison.OrdinalIgnoreCase)
             || string.Equals(usage, "webhook_outbound", StringComparison.OrdinalIgnoreCase)
             || string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase);
     }
@@ -192,7 +213,37 @@ public class AdminOAuthClientsController : ControllerBase
     private static bool RequiresClientCredentials(string usage)
     {
         return string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase)
-            || string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase);
+            || string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "send_api", StringComparison.OrdinalIgnoreCase);
+    }
+
+    private static bool UsesAuthorizationCodeFlow(string usage)
+    {
+        return string.Equals(usage, "webhook_outbound", StringComparison.OrdinalIgnoreCase);
+    }
+
+    private static (List<string> Uris, string? Error) NormalizeRedirectUris(List<string>? redirectUris)
+    {
+        if (redirectUris is null || redirectUris.Count == 0)
+        {
+            return ([], null);
+        }
+
+        var values = redirectUris
+            .Where(uri => !string.IsNullOrWhiteSpace(uri))
+            .Select(uri => uri.Trim())
+            .Distinct(StringComparer.OrdinalIgnoreCase)
+            .ToList();
+
+        foreach (var uri in values)
+        {
+            if (!Uri.TryCreate(uri, UriKind.Absolute, out _))
+            {
+                return ([], "redirect_uris must contain absolute URIs only.");
+            }
+        }
+
+        return (values, null);
     }
 
     private static void ApplyPermissions(OpenIddictApplicationDescriptor descriptor, string usage)
@@ -201,13 +252,19 @@ public class AdminOAuthClientsController : ControllerBase
         descriptor.Permissions.Add(OpenIddictConstants.Permissions.Endpoints.Token);
 
         if (string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase)
-            || string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase))
+            || string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "send_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 if (string.Equals(usage, "send_api", StringComparison.OrdinalIgnoreCase))
+            {
+                descriptor.Permissions.Add("scp:newsletter:send.write");
+                descriptor.Permissions.Add("scp:newsletter:send.read");
+            }
             else
             {
                 descriptor.Permissions.Add("scp:newsletter:events.write");

src/MemberCenter.Api/Controllers/NewsletterController.cs

@@ -95,6 +95,77 @@ public class NewsletterController : ControllerBase
         });
     }
 
+    [Authorize]
+    [HttpPost("one-click-unsubscribe-token")]
+    public async Task<IActionResult> IssueOneClickUnsubscribeToken([FromBody] IssueOneClickUnsubscribeTokenRequest request)
+    {
+        var hasTenantScope = HasScope(User, "newsletter:events.write");
+        var hasGlobalScope = HasScope(User, "newsletter:events.write.global");
+        if (!hasTenantScope && !hasGlobalScope)
+        {
+            return Forbid();
+        }
+
+        if (request.TenantId == Guid.Empty || request.ListId == Guid.Empty || request.SubscriberId == Guid.Empty)
+        {
+            return BadRequest("tenant_id, list_id, subscriber_id are required.");
+        }
+
+        if (!hasGlobalScope && TryGetTenantId(User, out var tokenTenantId) && tokenTenantId != request.TenantId)
+        {
+            return BadRequest("tenant_id does not match token tenant scope.");
+        }
+
+        var token = await _newsletterService.IssueOneClickUnsubscribeTokenAsync(request.TenantId, request.ListId, request.SubscriberId);
+        if (token is null)
+        {
+            return NotFound("Subscription not found.");
+        }
+
+        return Ok(new
+        {
+            unsubscribe_token = token
+        });
+    }
+
+    [Authorize]
+    [HttpPost("one-click-unsubscribe-tokens")]
+    public async Task<IActionResult> IssueOneClickUnsubscribeTokens([FromBody] IssueOneClickUnsubscribeTokensRequest request)
+    {
+        var hasTenantScope = HasScope(User, "newsletter:events.write");
+        var hasGlobalScope = HasScope(User, "newsletter:events.write.global");
+        if (!hasTenantScope && !hasGlobalScope)
+        {
+            return Forbid();
+        }
+
+        if (request.TenantId == Guid.Empty || request.ListId == Guid.Empty || request.SubscriberIds is null || request.SubscriberIds.Count == 0)
+        {
+            return BadRequest("tenant_id, list_id, subscriber_ids are required.");
+        }
+
+        if (request.SubscriberIds.Count > 1000)
+        {
+            return BadRequest("subscriber_ids exceeds maximum batch size (1000).");
+        }
+
+        if (!hasGlobalScope && TryGetTenantId(User, out var tokenTenantId) && tokenTenantId != request.TenantId)
+        {
+            return BadRequest("tenant_id does not match token tenant scope.");
+        }
+
+        var items = await _newsletterService.IssueOneClickUnsubscribeTokensAsync(request.TenantId, request.ListId, request.SubscriberIds);
+        return Ok(new
+        {
+            items = items.Select(x => new
+            {
+                subscriber_id = x.SubscriberId,
+                unsubscribe_token = x.UnsubscribeToken,
+                status = x.Status
+            })
+        });
+    }
+
     [HttpGet("preferences")]
     public async Task<IActionResult> Preferences([FromQuery(Name = "list_id")] Guid? listId, [FromQuery] string? email)
     {
@@ -175,4 +246,11 @@ public class NewsletterController : 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

@@ -13,15 +13,20 @@ namespace MemberCenter.Api.Controllers;
 [ApiController]
 public class TokenController : ControllerBase
 {
+    private readonly string _memberCenterAudience;
+    private readonly string _sendEngineAudience;
     private readonly UserManager<ApplicationUser> _userManager;
     private readonly SignInManager<ApplicationUser> _signInManager;
     private readonly IOpenIddictApplicationManager _applicationManager;
 
     public TokenController(
+        IConfiguration configuration,
         UserManager<ApplicationUser> userManager,
         SignInManager<ApplicationUser> signInManager,
         IOpenIddictApplicationManager applicationManager)
     {
+        _memberCenterAudience = configuration["Auth:MemberCenterAudience"] ?? "member_center_api";
+        _sendEngineAudience = configuration["Auth:SendEngineAudience"] ?? "send_engine_api";
         _userManager = userManager;
         _signInManager = signInManager;
         _applicationManager = applicationManager;
@@ -55,6 +60,7 @@ public class TokenController : ControllerBase
             var principal = await _signInManager.CreateUserPrincipalAsync(user);
             var scopes = request.Scope.GetScopesOrDefault();
             principal.SetScopes(scopes);
+            principal.SetResources(ResolveResources(scopes));
 
             foreach (var claim in principal.Claims)
             {
@@ -121,7 +127,9 @@ public class TokenController : ControllerBase
             }
 
             var principal = new ClaimsPrincipal(identity);
-            principal.SetScopes(request.Scope.GetScopesOrDefault());
+            var scopes = request.Scope.GetScopesOrDefault();
+            principal.SetScopes(scopes);
+            principal.SetResources(ResolveResources(scopes));
 
             foreach (var claim in principal.Claims)
             {
@@ -133,4 +141,35 @@ public class TokenController : ControllerBase
 
         return BadRequest("Unsupported grant type.");
     }
+
+    private IEnumerable<string> ResolveResources(IEnumerable<string> scopes)
+    {
+        var scopeSet = scopes as ISet<string> ?? new HashSet<string>(scopes, StringComparer.Ordinal);
+        if (scopeSet.Count == 0)
+        {
+            return [_memberCenterAudience];
+        }
+
+        var resources = new HashSet<string>(StringComparer.Ordinal);
+
+        if (scopeSet.Contains("newsletter:send.write") || scopeSet.Contains("newsletter:send.read"))
+        {
+            resources.Add(_sendEngineAudience);
+        }
+
+        if (scopeSet.Any(scope => scope.StartsWith("newsletter:", StringComparison.Ordinal) && scope is not "newsletter:send.write" && scope is not "newsletter:send.read")
+            || scopeSet.Contains(OpenIddictConstants.Scopes.OpenId)
+            || scopeSet.Contains(OpenIddictConstants.Scopes.Email)
+            || scopeSet.Contains(OpenIddictConstants.Scopes.Profile))
+        {
+            resources.Add(_memberCenterAudience);
+        }
+
+        if (resources.Count == 0)
+        {
+            resources.Add(_memberCenterAudience);
+        }
+
+        return resources;
+    }
 }

src/MemberCenter.Api/Program.cs

@@ -53,6 +53,16 @@ builder.Services.AddOpenIddict()
         options.SetAuthorizationEndpointUris("/oauth/authorize");
         options.SetTokenEndpointUris("/oauth/token", "/auth/login", "/auth/refresh");
         options.SetLogoutEndpointUris("/auth/logout");
+        var issuer = builder.Configuration["Auth:Issuer"];
+        if (!string.IsNullOrWhiteSpace(issuer))
+        {
+            if (!Uri.TryCreate(issuer, UriKind.Absolute, out var issuerUri))
+            {
+                throw new InvalidOperationException("Auth:Issuer must be an absolute URI.");
+            }
+
+            options.SetIssuer(issuerUri);
+        }
 
         options.AllowAuthorizationCodeFlow()
             .RequireProofKeyForCodeExchange();
@@ -67,12 +77,15 @@ builder.Services.AddOpenIddict()
             OpenIddictConstants.Scopes.Email,
             OpenIddictConstants.Scopes.Profile,
             "newsletter:list.read",
+            "newsletter:send.write",
+            "newsletter:send.read",
             "newsletter:events.read",
             "newsletter:events.write",
             "newsletter:events.write.global");
 
         options.AddDevelopmentEncryptionCertificate();
         options.AddDevelopmentSigningCertificate();
+        options.DisableAccessTokenEncryption();
 
         var aspNetCore = options.UseAspNetCore()
             .EnableAuthorizationEndpointPassthrough()

src/MemberCenter.Application/Abstractions/INewsletterService.cs

@@ -7,6 +7,8 @@ public interface INewsletterService
     Task<PendingSubscriptionResult?> SubscribeAsync(Guid listId, string email, Dictionary<string, object>? preferences);
     Task<SubscriptionDto?> ConfirmAsync(string token);
     Task<string?> IssueUnsubscribeTokenAsync(Guid listId, string email);
+    Task<string?> IssueOneClickUnsubscribeTokenAsync(Guid tenantId, Guid listId, Guid subscriberId);
+    Task<IReadOnlyList<OneClickUnsubscribeTokenResult>> IssueOneClickUnsubscribeTokensAsync(Guid tenantId, Guid listId, IReadOnlyList<Guid> subscriberIds);
     Task<SubscriptionDto?> UnsubscribeAsync(string token);
     Task<SubscriptionDto?> GetPreferencesAsync(Guid listId, string email);
     Task<SubscriptionDto?> UpdatePreferencesAsync(Guid listId, string email, Dictionary<string, object> preferences);

src/MemberCenter.Application/Models/Newsletter/SubscriptionDto.cs

@@ -11,3 +11,5 @@ public sealed record SubscriptionDto(
     DateTimeOffset CreatedAt);
 
 public sealed record PendingSubscriptionResult(SubscriptionDto Subscription, string ConfirmToken);
+
+public sealed record OneClickUnsubscribeTokenResult(Guid SubscriberId, string? UnsubscribeToken, string Status);

src/MemberCenter.Infrastructure/Services/NewsletterService.cs

@@ -15,8 +15,10 @@ public sealed class NewsletterService : INewsletterService
 {
     private const string ConfirmTokenPurpose = "confirm";
     private const string UnsubscribeTokenPurpose = "unsubscribe";
+    private const string OneClickUnsubscribeTokenPurpose = "one_click_unsubscribe";
     private const int ConfirmTokenTtlDays = 7;
     private const int UnsubscribeTokenTtlDays = 7;
+    private const int OneClickUnsubscribeTokenTtlDays = 7;
 
     private readonly MemberCenterDbContext _dbContext;
     private readonly IEmailBlacklistService _emailBlacklist;
@@ -154,10 +156,8 @@ public sealed class NewsletterService : INewsletterService
     public async Task<SubscriptionDto?> UnsubscribeAsync(string token)
     {
         _logger.LogInformation("Newsletter unsubscribe requested.");
-        var tokenHash = HashToken(token, UnsubscribeTokenPurpose);
+        var unsubscribeToken = await FindTokenAsync(token, UnsubscribeTokenPurpose)
-        var unsubscribeToken = await _dbContext.UnsubscribeTokens
+            ?? await FindTokenAsync(token, OneClickUnsubscribeTokenPurpose);
-            .Include(t => t.Subscription)
-            .FirstOrDefaultAsync(t => t.TokenHash == tokenHash && t.ConsumedAt == null);
 
         if (unsubscribeToken?.Subscription is null)
         {
@@ -230,6 +230,84 @@ public sealed class NewsletterService : INewsletterService
         return token;
     }
 
+    public async Task<string?> IssueOneClickUnsubscribeTokenAsync(Guid tenantId, Guid listId, Guid subscriberId)
+    {
+        var items = await IssueOneClickUnsubscribeTokensAsync(tenantId, listId, new[] { subscriberId });
+        return items.FirstOrDefault()?.UnsubscribeToken;
+    }
+
+    public async Task<IReadOnlyList<OneClickUnsubscribeTokenResult>> IssueOneClickUnsubscribeTokensAsync(
+        Guid tenantId,
+        Guid listId,
+        IReadOnlyList<Guid> subscriberIds)
+    {
+        var requested = subscriberIds
+            .Where(x => x != Guid.Empty)
+            .Distinct()
+            .ToList();
+
+        if (requested.Count == 0)
+        {
+            return Array.Empty<OneClickUnsubscribeTokenResult>();
+        }
+
+        var subscriptions = await (
+            from s in _dbContext.NewsletterSubscriptions
+            join l in _dbContext.NewsletterLists on s.ListId equals l.Id
+            where l.TenantId == tenantId && s.ListId == listId && requested.Contains(s.Id)
+            select s)
+            .ToListAsync();
+
+        var byId = subscriptions.ToDictionary(x => x.Id, x => x);
+        var normalizedEmails = subscriptions
+            .Select(s => s.Email.ToLowerInvariant())
+            .Distinct()
+            .ToList();
+
+        var blacklistedEmails = await _dbContext.EmailBlacklist
+            .Where(x => normalizedEmails.Contains(x.Email))
+            .Select(x => x.Email)
+            .ToListAsync();
+        var blacklistedSet = blacklistedEmails.ToHashSet(StringComparer.OrdinalIgnoreCase);
+
+        var results = new List<OneClickUnsubscribeTokenResult>(requested.Count);
+        foreach (var subscriberId in requested)
+        {
+            if (!byId.TryGetValue(subscriberId, out var subscription))
+            {
+                results.Add(new OneClickUnsubscribeTokenResult(subscriberId, null, "not_found"));
+                continue;
+            }
+
+            if (blacklistedSet.Contains(subscription.Email))
+            {
+                results.Add(new OneClickUnsubscribeTokenResult(subscriberId, null, "blacklisted"));
+                continue;
+            }
+
+            var token = CreateToken();
+            _dbContext.UnsubscribeTokens.Add(new UnsubscribeToken
+            {
+                Id = Guid.NewGuid(),
+                SubscriptionId = subscription.Id,
+                TokenHash = HashToken(token, OneClickUnsubscribeTokenPurpose),
+                ExpiresAt = DateTimeOffset.UtcNow.AddDays(OneClickUnsubscribeTokenTtlDays)
+            });
+
+            results.Add(new OneClickUnsubscribeTokenResult(subscriberId, token, "issued"));
+        }
+
+        await _dbContext.SaveChangesAsync();
+        _logger.LogInformation(
+            "One-click token batch issued. tenant_id={TenantId}, list_id={ListId}, requested={RequestedCount}, issued={IssuedCount}",
+            tenantId,
+            listId,
+            requested.Count,
+            results.Count(x => string.Equals(x.Status, "issued", StringComparison.OrdinalIgnoreCase)));
+
+        return results;
+    }
+
     public async Task<SubscriptionDto?> GetPreferencesAsync(Guid listId, string email)
     {
         if (await _emailBlacklist.IsBlacklistedAsync(email))

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

@@ -61,7 +61,7 @@ public class OAuthClientsController : Controller
     {
         if (!IsValidUsage(model.Usage))
         {
-            ModelState.AddModelError(nameof(model.Usage), "Usage must be tenant_api, webhook_outbound, or platform_service.");
+            ModelState.AddModelError(nameof(model.Usage), "Usage must be tenant_api, send_api, webhook_outbound, or platform_service.");
         }
 
         if (!IsTenantOptionalUsage(model.Usage) && (!model.TenantId.HasValue || model.TenantId.Value == Guid.Empty))
@@ -75,6 +75,16 @@ public class OAuthClientsController : Controller
             ModelState.AddModelError(nameof(model.ClientType), "Client type must be confidential for this usage.");
         }
 
+        var redirectUris = NormalizeRedirectUris(model.RedirectUris, out var redirectUriError);
+        if (!string.IsNullOrWhiteSpace(redirectUriError))
+        {
+            ModelState.AddModelError(nameof(model.RedirectUris), redirectUriError);
+        }
+        if (UsesAuthorizationCodeFlow(model.Usage) && redirectUris.Count == 0)
+        {
+            ModelState.AddModelError(nameof(model.RedirectUris), "Redirect URI is required for webhook_outbound usage.");
+        }
+
         if (!ModelState.IsValid)
         {
             model.Tenants = await _tenantService.ListAsync();
@@ -92,7 +102,7 @@ public class OAuthClientsController : Controller
             descriptor.ClientSecret = clientSecret;
         }
 
-        foreach (var uri in model.RedirectUris.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries))
+        foreach (var uri in redirectUris)
         {
             descriptor.RedirectUris.Add(new Uri(uri));
         }
@@ -146,7 +156,7 @@ public class OAuthClientsController : Controller
     {
         if (!IsValidUsage(model.Usage))
         {
-            ModelState.AddModelError(nameof(model.Usage), "Usage must be tenant_api, webhook_outbound, or platform_service.");
+            ModelState.AddModelError(nameof(model.Usage), "Usage must be tenant_api, send_api, webhook_outbound, or platform_service.");
         }
 
         if (!IsTenantOptionalUsage(model.Usage) && (!model.TenantId.HasValue || model.TenantId.Value == Guid.Empty))
@@ -160,6 +170,16 @@ public class OAuthClientsController : Controller
             ModelState.AddModelError(nameof(model.ClientType), "Client type must be confidential for this usage.");
         }
 
+        var redirectUris = NormalizeRedirectUris(model.RedirectUris, out var redirectUriError);
+        if (!string.IsNullOrWhiteSpace(redirectUriError))
+        {
+            ModelState.AddModelError(nameof(model.RedirectUris), redirectUriError);
+        }
+        if (UsesAuthorizationCodeFlow(model.Usage) && redirectUris.Count == 0)
+        {
+            ModelState.AddModelError(nameof(model.RedirectUris), "Redirect URI is required for webhook_outbound usage.");
+        }
+
         if (!ModelState.IsValid)
         {
             model.Tenants = await _tenantService.ListAsync();
@@ -179,7 +199,7 @@ public class OAuthClientsController : Controller
         descriptor.ClientType = model.ClientType;
         ApplyPermissions(descriptor, model.Usage);
         descriptor.RedirectUris.Clear();
-        foreach (var uri in model.RedirectUris.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries))
+        foreach (var uri in redirectUris)
         {
             descriptor.RedirectUris.Add(new Uri(uri));
         }
@@ -242,6 +262,7 @@ public class OAuthClientsController : Controller
     private static bool IsValidUsage(string usage)
     {
         return string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "send_api", StringComparison.OrdinalIgnoreCase)
             || string.Equals(usage, "webhook_outbound", StringComparison.OrdinalIgnoreCase)
             || string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase);
     }
@@ -254,7 +275,38 @@ public class OAuthClientsController : Controller
     private static bool RequiresClientCredentials(string usage)
     {
         return string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase)
-            || string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase);
+            || string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "send_api", StringComparison.OrdinalIgnoreCase);
+    }
+
+    private static bool UsesAuthorizationCodeFlow(string usage)
+    {
+        return string.Equals(usage, "webhook_outbound", StringComparison.OrdinalIgnoreCase);
+    }
+
+    private static List<string> NormalizeRedirectUris(string redirectUrisText, out string? error)
+    {
+        error = null;
+        if (string.IsNullOrWhiteSpace(redirectUrisText))
+        {
+            return [];
+        }
+
+        var values = redirectUrisText
+            .Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
+            .Distinct(StringComparer.OrdinalIgnoreCase)
+            .ToList();
+
+        foreach (var value in values)
+        {
+            if (!Uri.TryCreate(value, UriKind.Absolute, out _))
+            {
+                error = "All redirect URIs must be absolute URIs.";
+                return [];
+            }
+        }
+
+        return values;
     }
 
     private static OpenIddictApplicationDescriptor BuildDescriptor(string clientId, string name, string clientType, string usage)
@@ -276,13 +328,19 @@ public class OAuthClientsController : Controller
         descriptor.Permissions.Add(OpenIddictConstants.Permissions.Endpoints.Token);
 
         if (string.Equals(usage, "platform_service", StringComparison.OrdinalIgnoreCase)
-            || string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase))
+            || string.Equals(usage, "tenant_api", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(usage, "send_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 if (string.Equals(usage, "send_api", StringComparison.OrdinalIgnoreCase))
+            {
+                descriptor.Permissions.Add("scp:newsletter:send.write");
+                descriptor.Permissions.Add("scp:newsletter:send.read");
+            }
             else
             {
                 descriptor.Permissions.Add("scp:newsletter:events.write");

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

@@ -26,13 +26,53 @@
   <label>Usage</label>
   <select asp-for="Usage">
     <option value="tenant_api">tenant_api</option>
+    <option value="send_api">send_api</option>
     <option value="webhook_outbound">webhook_outbound</option>
     <option value="platform_service">platform_service</option>
   </select>
   <span asp-validation-for="Usage"></span>
 
-  <label>Redirect URIs (comma-separated)</label>
+  <label>Redirect URIs (comma-separated, only for webhook_outbound)</label>
   <input asp-for="RedirectUris" />
+  <span asp-validation-for="RedirectUris"></span>
 
   <button type="submit">Save</button>
 </form>
+
+<script>
+  (function () {
+    const usage = document.getElementById("Usage");
+    const redirect = document.getElementById("RedirectUris");
+    const clientType = document.getElementById("ClientType");
+    if (!usage || !redirect || !clientType) return;
+
+    function syncRedirectInputState() {
+      const usageValue = usage.value;
+      const needsRedirect = usageValue === "webhook_outbound";
+      const requiresConfidential = usageValue === "tenant_api"
+        || usageValue === "send_api"
+        || usageValue === "platform_service";
+
+      redirect.disabled = !needsRedirect;
+      if (!needsRedirect) {
+        redirect.value = "";
+      }
+
+      if (requiresConfidential) {
+        clientType.value = "confidential";
+        const publicOption = clientType.querySelector('option[value="public"]');
+        if (publicOption) {
+          publicOption.disabled = true;
+        }
+      } else {
+        const publicOption = clientType.querySelector('option[value="public"]');
+        if (publicOption) {
+          publicOption.disabled = false;
+        }
+      }
+    }
+
+    usage.addEventListener("change", syncRedirectInputState);
+    syncRedirectInputState();
+  })();
+</script>

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

@@ -26,13 +26,53 @@
   <label>Usage</label>
   <select asp-for="Usage">
     <option value="tenant_api">tenant_api</option>
+    <option value="send_api">send_api</option>
     <option value="webhook_outbound">webhook_outbound</option>
     <option value="platform_service">platform_service</option>
   </select>
   <span asp-validation-for="Usage"></span>
 
-  <label>Redirect URIs (comma-separated)</label>
+  <label>Redirect URIs (comma-separated, only for webhook_outbound)</label>
   <input asp-for="RedirectUris" />
+  <span asp-validation-for="RedirectUris"></span>
 
   <button type="submit">Save</button>
 </form>
+
+<script>
+  (function () {
+    const usage = document.getElementById("Usage");
+    const redirect = document.getElementById("RedirectUris");
+    const clientType = document.getElementById("ClientType");
+    if (!usage || !redirect || !clientType) return;
+
+    function syncRedirectInputState() {
+      const usageValue = usage.value;
+      const needsRedirect = usageValue === "webhook_outbound";
+      const requiresConfidential = usageValue === "tenant_api"
+        || usageValue === "send_api"
+        || usageValue === "platform_service";
+
+      redirect.disabled = !needsRedirect;
+      if (!needsRedirect) {
+        redirect.value = "";
+      }
+
+      if (requiresConfidential) {
+        clientType.value = "confidential";
+        const publicOption = clientType.querySelector('option[value="public"]');
+        if (publicOption) {
+          publicOption.disabled = true;
+        }
+      } else {
+        const publicOption = clientType.querySelector('option[value="public"]');
+        if (publicOption) {
+          publicOption.disabled = false;
+        }
+      }
+    }
+
+    usage.addEventListener("change", syncRedirectInputState);
+    syncRedirectInputState();
+  })();
+</script>