[PM-29142] Config for SSO cookie vending (#6880)

This config may be used when a load balancer in front of Bitwarden is
first verifying an auth cookie issued by an IdP before proxying the
request to Bitwarden.

dev/secrets.json.example

@@ -39,6 +39,14 @@
     },
     "licenseDirectory": "<full path to license directory>",
     "enableNewDeviceVerification": true,
-    "enableEmailVerification": true
+    "enableEmailVerification": true,
+    "communication": {
+      "bootstrap": "none",
+      "ssoCookieVendor": {
+        "idpLoginUrl": "",
+        "cookieName": "",
+        "cookieDomain": ""
+      }
+    }
   }
 }