Terraform IAM secret key decode

Hi All,
Now I am interlocking Terraform and go-based server.

In here, I want to copy IAM system by using this… And faced a problem.

Terraform provider has access_key and secret_key, and I want to use these two keys to implement authorization solution at go server.
And I can confirmed my access_key is contained at header’s credential, but problem is ‘secret_key’.

In my inference, it would be encoded and stored at Signature… but I cannot confirm that.

Is secret_key stored at Signature?? If not, where does it exists in header side??
And I wonder if it can be decoded at my server…