401 Unauthorized error while attempting to pull a docker image off gcr.io using terraform

Question

First: I am very new to GCP, Terraform so pardon me if this is a dumb question / has been answered before. I have tried googling for it and havent got anywhere.

I am trying to pull a docker image from gcr.io to refer to its SHA. In my terraform scripts, I am hoping to deploy to Cloud Run when the SHA changes - the actual build happens in my Github Actions outside of Terraform. But when the action fires, I get a 401 Unauthorized error! The rest of the terraform actions with google provider resources work fine.

Note: my registry is private.

In order to achieve this, I am using the package kreuzwerker/docker: Pasting relevant sections of my scripts here:

Terraform script:

terraform {
    required_providers {
        google = {
            source = "hashicorp/google"
            version = "~> 5.0"
        }
        cloudflare = {
            source  = "cloudflare/cloudflare"
            version = "~> 4.0"
        }    
        docker = {
            source  = "kreuzwerker/docker"
            version = "~> 3.0"
        }
    }
}

...

provider "docker" {
    registry_auth {
        address  = "gcr.io"
        username = "oauth2accesstoken"
        password = data.google_client_config.current-user.access_token
    }
}

... 

data "docker_registry_image" "backend_services_image_metadata" {
    name = "gcr.io/${var.project_id}/${var.repo-name}:${var.repo-tag}"
}

data "google_container_registry_image" "backend_services_image_data" {
    name   = var.services-image-repo-name
    digest = data.docker_registry_image.backend_services_image_metadata.sha256_digest
}

...

When i execute this script, I get the following error:

Error: Got error when attempting to fetch image version project-XXXX/repo-XXXX:latest from registry: Bad credentials: 401 Unauthorized

I expected this to work and return me a SHA