Values.MasterUserOptionsSourceCredentials for the master user for a domain.
type nonrec t = {masterUserARN : ARN.t option;Amazon Resource Name (ARN) for the master user. Only specify if InternalUserDatabaseEnabled is false.
*)masterUserName : Username.t option;User name for the master user. Only specify if InternalUserDatabaseEnabled is true.
*)masterUserPassword : Password.t option;Password for the master user. Only specify if InternalUserDatabaseEnabled is true.
*)}