To authenticate itself to the ACS? Or for the ACS to authenticate itself to the CPE?
Here is the default inform provision. It sets the username/password for ACS to CPE authentication.
// Device ID as user name
const username = declare("DeviceID.ID", {value: 1}).value[0]
// Password will be fixed for a given device because Math.random() is seeded with device ID by default.
const password = Math.trunc(Math.random() * Number.MAX_SAFE_INTEGER).toString(36);
const informInterval = 300;
// Refresh values daily
const daily = Date.now(86400000);
// Unique inform offset per device for better load distribution
const informTime = daily % 86400000;
declare("InternetGatewayDevice.ManagementServer.ConnectionRequestUsername", {value: daily}, {value: username});
declare("InternetGatewayDevice.ManagementServer.ConnectionRequestPassword", {value: daily}, {value: password});
declare("InternetGatewayDevice.ManagementServer.PeriodicInformEnable", {value: daily}, {value: true});
declare("InternetGatewayDevice.ManagementServer.PeriodicInformInterval", {value: daily}, {value: informInterval});
declare("InternetGatewayDevice.ManagementServer.PeriodicInformTime", {value: daily}, {value: informTime});
declare("Device.ManagementServer.ConnectionRequestUsername", {value: daily}, {value: username});
declare("Device.ManagementServer.ConnectionRequestPassword", {value: daily}, {value: password});
declare("Device.ManagementServer.PeriodicInformEnable", {value: daily}, {value: true});
declare("Device.ManagementServer.PeriodicInformInterval", {value: daily}, {value: informInterval});
declare("Device.ManagementServer.PeriodicInformTime", {value: daily}, {value: informTime});