fix(yar): add missing session id property (#27761)

types/yar/index.d.ts

@@ -105,12 +105,17 @@ declare namespace yar {
              * an optional function to create custom session IDs.
              * Must retun a string and have the signature function (request) where:
              * request - (optional) is the original request received from the client.
+             * Defaults to uuidv4
              */
             customSessionIDGenerator?(req: Request): string;
         };
     }
 
     interface Yar {
+        /**
+         * Session id, see `customSessionIDGenerator`.
+         */
+        readonly id: string;
         /**
          * clears the session and assigns a new session id.
          */

types/yar/yar-tests.ts

@@ -18,7 +18,10 @@ async function boot() {
         method: 'get',
         handler(request: Request) {
             const example = request.yar.get('example');
-            return example.key;
+            return {
+                id: request.yar.id,
+                key: example.key,
+            };
         },
     });
 }