You will need a Replicon user account to call the services for your integration. Use HTTP Basic authentication to connect using the account.
The permissions given to the account apply to both the application and the web services. For example, if the user has permission to edit timesheets as a Billing Manager, the integration will be able to call services to edit timesheets as well. Therefore, you may want to set up a separate user account for the integration with full permissions for the system.