Add explanation in the docs on how to configure token based authentic…

…ation

Signed-off-by: Georgi Panov <[email protected]>

docs/spec/v1beta3/providers.md

@@ -919,12 +919,21 @@ and [TLS certificates](#tls-certificates).
 
 ###### Prometheus Alertmanager example
 
+To configure a Provider for Prometheus Alertmanager, you can authenticate using Basic Authentication or a Bearer Token. 
+Both authentication methods are supported, and you can choose the one that best fits your setup.
+
 To configure a Provider for Prometheus Alertmanager, create a Secret with [the
 `address`](#address-example) set to the Prometheus Alertmanager [HTTP API
 URL](https://prometheus.io/docs/alerting/latest/https/#http-traffic)
 including Basic Auth credentials, and a `alertmanager` Provider with a [Secret
 reference](#secret-reference).
 
+Basic Authentication: 
+Create a Secret with [the `address`](#address-example) set to the Prometheus Alertmanager [HTTP API
+URL](https://prometheus.io/docs/alerting/latest/https/#http-traffic)
+including Basic Auth credentials, and a `alertmanager` Provider with a [Secret
+reference](#secret-reference).
+
 ```yaml
 ---
 apiVersion: notification.toolkit.fluxcd.io/v1beta3
@@ -945,6 +954,8 @@ metadata:
 stringData:
     address: https://username:password@<alertmanager-url>/api/v2/alerts/"
 ```
+Bearer Token Authentication:
+Create a Secret with [the `token`](#token-example)
 
 ##### Webex