A string array containing the names of all the roles stored in the data source for the configured applicationName.
RoleProvider.GetAllRoles is called by the Roles.GetAllRoles method of the System.Web.Security.Roles class to retrieve a list of role names from the data source. Only the roles for the specified RoleProvider.ApplicationName are retrieved.
If no roles exist for the configured applicationName, we recommend that your provider return a string array with no elements.