docs: add links to references

Author: kenjis

docs/getting_started/authenticators.md

@@ -6,11 +6,14 @@ Shield provides the following Authenticators:
 
 - **Session** authenticator provides traditional ID/Password authentication.
   It uses username/email/password to authenticate against and stores the user
-  information in the session. See [Using Session Authenticator](../quick_start_guide/using_session_auth.md) for usage.
+  information in the session. See [Using Session Authenticator](../quick_start_guide/using_session_auth.md)
+  and [Session Authenticator](../references/authentication/session.md) for usage.
 - **AccessTokens** authenticator provides stateless authentication using Personal
   Access Tokens passed in the HTTP headers.
-  See [Protecting an API with Access Tokens](../guides/api_tokens.md) for usage.
+  See [Protecting an API with Access Tokens](../guides/api_tokens.md) and
+  [Access Token Authenticator](../references/authentication/tokens.md) for usage.
 - **HmacSha256** authenticator provides stateless authentication using HMAC Keys.
-  See [Protecting an API with HMAC Keys](../guides/api_hmac_keys.md) for usage.
+  See [Protecting an API with HMAC Keys](../guides/api_hmac_keys.md) and
+  [HMAC SHA256 Token Authenticator](../references/authentication/hmac.md) for usage.
 - **JWT** authenticator provides stateless authentication using JSON Web Token. To use this,
   you need additional setup. See [JWT Authentication](../addons/jwt.md).