TAX-2677: docs(tax) - Add X-Auth-Token security scheme with MANAGE_TAX permission

Refs TAX-2677
Co-Authored-By: Claude <noreply@anthropic.com>

Author: bc-vincent-zhao

reference/tax_classes.v3.yaml

@@ -25,6 +25,9 @@ servers:
         description: Permanent ID of the BigCommerce store.
     description: BigCommerce API Gateway
 
+security:
+  - X-Auth-Token: []
+
 tags:
   - name: Tax Classes
     description: Create, update, and delete tax classes.
@@ -228,6 +231,32 @@ paths:
                 $ref: '#/components/schemas/ProblemResponseEnvelope'
 
 components:
+  securitySchemes:
+    X-Auth-Token:
+      name: X-Auth-Token
+      description: |-
+        ### OAuth scopes
+
+        | UI Name | Permission | Parameter |
+        |:--------|:-----------|:----------|
+        | Tax | modify | `MANAGE_TAX` |
+
+        ### Authentication header
+
+        | Header | Argument | Description |
+        |:-------|:---------|:------------|
+        | `X-Auth-Token` | `access_token` | For more about API accounts that generate `access_token`s, see our [Guide to API Accounts](/docs/start/authentication/api-accounts). |
+
+        ### Further reading
+
+        For example requests and more information about authenticating BigCommerce APIs, see [Authentication and Example Requests](/docs/start/authentication#x-auth-token-header-example-requests).
+
+        For more about BigCommerce OAuth scopes, see our [Guide to API Accounts](/docs/start/authentication/api-accounts#oauth-scopes).
+
+        For a list of API status codes, see [API Status Codes](/docs/start/about/status-codes).
+      type: apiKey
+      in: header
+
   schemas:
     TaxClassCreateBatch:
       type: array