Merge branch 'site-key-authx' into 'master'

Document passing a site key in AuthX

See merge request documentation/docs/dev!1050

docs/framework/authx.md

@@ -172,6 +172,11 @@ A *guard* limits access to AuthX authentication services.  By default, a user wh
 
 * __Permission__: Check if the user has permission `authenticate with password` or `authenticate with api key`.
 * __Site Key__: Check if the user knows the [secret site key](https://docs.civicrm.org/sysadmin/en/latest/setup/secret-keys/#civicrm_site_key).
+??? question "How can I send the site key?"
+    The site key can be passed with either:
+
+    * X-Header: `X-Civi-Key: 1234abc`
+    * Parameter: `?_authxSiteKey=1234abc`
 
 ??? question "Why support both guards?"