Merge pull request #211716 from cemateia/update-docs-custom-token-expiration

Update identity-model.md for custom token expiration feature

Author: prmerger-automator[bot]

articles/communication-services/concepts/identity-model.md

@@ -56,7 +56,9 @@ The properties of an access token are:
 * Expiration.
 * Scopes.
 
-An access token is always valid for 24 hours. After it expires, the access token is invalidated and can't be used to access any primitive.
+An access token is valid for a period of time between 1 and 24 hours. After it expires, the access token is invalidated and can't be used to access any primitive.
+To generate a token with a custom validity, specify the desired validity period when generating the token. If no custom validity is specified, the token will be valid for 24 hours. 
+We recommend using short lifetime tokens for one-off meetings and longer lifetime tokens for agents using the application for longer periods of time.
 
 An identity needs a way to request a new access token from a server-side service. The *scope* parameter defines a nonempty set of primitives that can be used. Azure Communication Services supports the following scopes for access tokens.