Authenticate & Refresh Token

[Vivek2s]

Hello Sir/Mam,
I making an Integration of infusionsoft to create contacts for insfusionsoft users.To make this possible I want to know how I can authenticate the user & create Contacts & also please tell which service or function I use for refresh token.

Thank you

[itsdevweb3]

I have same problem. I am not sure why that has not this problem.