Document Profile API endpoints

docs/authenticate/api/30-profile-api.md

@@ -1,3 +1,59 @@
 # Profile API
 
-TODO.
+The Profile API handles individual user data management. It allows users to view their dashboard settings, update their account passwords, or configure security keys. 
+
+To tell the server what you want to do, your request body must include a `"kind"` key specifying your exact operation.
+
+### Fetching User Profile Information
+
+Use this endpoint to grab the active user's account details and metadata.
+
+* **Method:** `POST`
+* **Endpoint Path:** `/api/profile`
+* **Content Type:** `application/json`
+
+#### What to send in the request body:
+```json
+{
+  "kind": "fetch_user_info"
+}
+```
+
+#### What a successful response looks like (200 OK):
+```json
+{
+  "status": "success",
+  "user_info": {
+    "username": "developer_user",
+    "email": "user@example.com",
+    "name": "Alex Smith"
+  },
+  "timestamp": "2026-06-28T19:30:00Z"
+}
+```
+
+---
+
+### Updating a User Password
+
+Use this configuration to securely update an active user account password.
+
+* **Method:** `POST`
+* **Endpoint Path:** `/api/profile`
+
+#### What to send in the request body:
+```json
+{
+  "kind": "update_user_password",
+  "current_password": "old_password_123",
+  "new_password": "secure_new_password_456"
+}
+```
+
+#### What a successful response looks like (200 OK):
+```json
+{
+  "status": "success",
+  "message": "Password changed successfully."
+}
+```