[MINOR] add payload example for ease of copying (#519)

* add payload example for ease of copying

Signed-off-by: Sally MacFarlane <sally.macfarlane@consensys.net>

* edit

Signed-off-by: Madeline Murray <madeline.taylor@gmail.com>

Co-authored-by: Madeline Murray <madeline.taylor@gmail.com>

docs/HowTo/Interact/APIs/Authentication.md

@@ -162,6 +162,16 @@ Each payload for the JWT contains:
 * Optionally, the tenant's Orion public key using `privacyPublicKey`. Only used for
   [multi-tenancy](../../../Concepts/Privacy/Multi-Tenancy.md).
 
+!!! example "Example payload"
+
+    ```json
+    {
+      "permissions": ["*:*"],
+      "privacyPublicKey": "2UKH3VJThkOoKskrLFpwoxCnnRARyobV1bEdgseFHTs=",
+      "exp": 1600899999002
+    }
+    ```
+
 The following example uses the [JWT.io](https://jwt.io/) website to create a JWT for testing
 purposes.