[Doc] add scope explanations (apache#12380)

* [Doc] add scope explanations

* update

site2/docs/security-oauth2.md

@@ -29,6 +29,7 @@ The following table lists parameters supported for the `client credentials` auth
 | `issuerUrl` | URL of the authentication provider which allows the Pulsar client to obtain an access token | `https://accounts.google.com` | Required |
 | `privateKey` | URL to a JSON credentials file  | Support the following pattern formats: <br> <li> `file:///path/to/file` <li>`file:/path/to/file` <li> `data:application/json;base64,<base64-encoded value>` | Required |
 | `audience`  | An OAuth 2.0 "resource server" identifier for the Pulsar cluster | `https://broker.example.com` | Required |
+| `scope` |  Scope of an access request. <br />For more more information, see [access token scope](https://datatracker.ietf.org/doc/html/rfc6749#section-3.3). | api://pulsar-cluster-1/.default | Optional |
 
 The credentials file contains service account credentials used with the client authentication type. The following shows an example of a credentials file `credentials_file.json`.
 
@@ -98,7 +99,7 @@ PulsarClient client = PulsarClient.builder()
 
 ### C++ client
 
-The C++ client is similar to the Java client. You need to provide parameters of `issuerUrl`, `private_key` (the credentials file path), and the audience.
+The C++ client is similar to the Java client. You need to provide parameters of `issuerUrl`, `private_key` (the credentials file path), and `audience`.
 
 ```c++
 #include <pulsar/Client.h>