------------------------------------------------------------
-- create credential

USE [master]
GO
CREATE CREDENTIAL [MyAuthenticatedUser] 
WITH IDENTITY = N'MyComputer\MyAuthenticatedUser', SECRET = N'mypassword'
GO

------------------------------------------------------------
-- create proxy

USE [msdb]
GO

EXEC msdb.dbo.sp_add_proxy 
    @proxy_name = N'MyAuthenticatedUser',
    @credential_name = N'MyAuthenticatedUser',
    @enabled = 1
GO

EXEC msdb.dbo.sp_grant_proxy_to_subsystem 
    @proxy_name = N'MyAuthenticatedUser',
    @subsystem_id = 12
GO

------------------------------------------------------------
-- create job

USE [msdb]
GO

BEGIN TRANSACTION
DECLARE @ReturnCode INT
SELECT  @ReturnCode = 0
IF NOT EXISTS ( SELECT  name
                FROM    msdb.dbo.syscategories
                WHERE   name = N'[Uncategorized (Local)]'
                        AND category_class = 1 ) 
    BEGIN
        EXEC @ReturnCode = msdb.dbo.sp_add_category 
            @class = N'JOB',
            @type = N'LOCAL',
            @name = N'[Uncategorized (Local)]'
        IF (
            @@ERROR <> 0
            OR @ReturnCode <> 0
           ) 
            GOTO QuitWithRollback

    END

DECLARE @jobId BINARY(16)
EXEC @ReturnCode = msdb.dbo.sp_add_job 
    @job_name = N'test ps',
    @enabled = 1,
    @notify_level_eventlog = 0,
    @notify_level_email = 0,
    @notify_level_netsend = 0,
    @notify_level_page = 0,
    @delete_level = 0,
    @description = N'No description available.',
    @category_name = N'[Uncategorized (Local)]',
    @owner_login_name = N'sa',
    @job_id = @jobId OUTPUT
IF (
    @@ERROR <> 0
    OR @ReturnCode <> 0
   ) 
    GOTO QuitWithRollback
EXEC @ReturnCode = msdb.dbo.sp_add_jobstep 
    @job_id = @jobId,
    @step_name = N'test',
    @step_id = 1,
    @cmdexec_success_code = 0,
    @on_success_action = 1,
    @on_success_step_id = 0,
    @on_fail_action = 2,
    @on_fail_step_id = 0,
    @retry_attempts = 0,
    @retry_interval = 0,
    @os_run_priority = 0,
    @subsystem = N'PowerShell',
    @command = N'$Volumes = get-WMIObject WIN32_Volume |where-object {$_.FreeSpace -ne $null};
$Volumes',
    @database_name = N'master',
    @flags = 0,
    @proxy_name = N'MyAuthenticatedUser'
IF (
    @@ERROR <> 0
    OR @ReturnCode <> 0
   ) 
    GOTO QuitWithRollback
EXEC @ReturnCode = msdb.dbo.sp_update_job 
    @job_id = @jobId,
    @start_step_id = 1
IF (
    @@ERROR <> 0
    OR @ReturnCode <> 0
   ) 
    GOTO QuitWithRollback
EXEC @ReturnCode = msdb.dbo.sp_add_jobserver 
    @job_id = @jobId,
    @server_name = N'(local)'
IF (
    @@ERROR <> 0
    OR @ReturnCode <> 0
   ) 
    GOTO QuitWithRollback
COMMIT TRANSACTION
GOTO EndSave
QuitWithRollback:
IF (@@TRANCOUNT > 0) 
    ROLLBACK TRANSACTION
EndSave:

GO