Invalid CSRF token when submitting a form

Thank you for the suggestions, it's really helpful.

I have been googling it but with something so important its hard to sort out the good ones from the bad.

I used Ion Auth, works like a charm

Built with codeigniter (thank you Codeigniter Team)

Both Ion Auth and Community Auth are good choices. The brains behind Community Auth hangs out around here which can come in handy.