How does AWS IAM can decode signatures sent from terraform?

Now I am trying to copy IAM by using go, terraform, and Vault. But I encountered problem with terraform's secret_key

this is my terraform provider code...

provider "aws" {  
  alias = "aws_2"

  secret_key = "my secret key..." 
  access_key = "my access key..." 

  ###  elbv2 ###
  region = "ap-northeast-2"
                                                                                                                                                                                                               
}

with this, this terraform is communicating with my go server. And I confirmed access key is contained at header's authorization states, but I think my secret key may be located at signature with encoded state.

Problem is that, terraform's signature encrypt algorithm is SHA256, so I don't have any solution that can decrypt it.

How does AWS decrypt this, and can I copy it?? If not, is there any solution that can match terraform's secret_key and go server's secret_key?

Thank you.