You've not mentioned exactly how you're authenticating, but regardless, here's a script for creating a login, credential and proxy and granting permissions to SSIS packages:
CREATE LOGIN [MyLogin] FROM WINDOWS WITH DEFAULT_DATABASE=[master], DEFAULT_LANGUAGE=[us_english]
GO
GRANT CONNECT TO [MyLogin]
go
CREATE ROLE MyRole
GO
EXEC sp_addrolemember @membername = N'MyLogin', @rolename = N'MyRole'
GO
CREATE CREDENTIAL MyCredential WITH IDENTITY = 'MyLogin', SECRET = 'MyPassword';
GO
USE [msdb]
GO
EXEC msdb.dbo.sp_add_proxy @proxy_name=N'MyProxy',@credential_name=N'MyCredential',
@enabled=1
GO
EXEC msdb.dbo.sp_grant_proxy_to_subsystem @proxy_name=N'MyProxy', @subsystem_id=11
GO
EXEC msdb.dbo.sp_grant_login_to_proxy @proxy_name=N'MyProxy', @login_name=N'MyLogin'
GO
CREATE ROLE MyRole
GO
EXEC sp_addrolemember @membername = N'MyRole', @rolename = N'db_ssisadmin'
GO
EXEC sp_addrolemember @membername = N'MyRole', @rolename = N'db_ssisoperator'
GO
EXEC sp_addrolemember @membername = N'MyLogin', @rolename = N'MyRole'
GO