Updates API Authentication section (#4068) (#4136)

(cherry picked from commit d4e0844)

Co-authored-by: natasha-moore-elastic <137783811+natasha-moore-elastic@users.noreply.github.com>

docs/siem-apis.asciidoc

@@ -48,8 +48,17 @@ NOTE: You can find space URL identifiers on
 [float]
 === Authentication
 
-Token-based authentication, using the same username and password used to log in
-to the Kibana UI, is required to access the APIs.
+The {elastic-sec} APIs support key- and token-based authentication.
+
+[float]
+==== Key-based authentication
+
+To use key-based authentication, create an {kibana-ref}/api-keys.html[API key], then specify the key in the header of your API calls.
+
+[float]
+==== Token-based authentication
+
+For token-based authentication, use the same username and password that you use to log in to the {kib} UI. In a given HTTP tool, and when available, you can select to use its **Basic Authentication** option, which is where the username and password are stored in order to be passed as part of the call.
 
 [float]
 === API calls