Use docker expiration string from auth config (#196)

Description of changes:
Just checking the existence of the authorization string in Docker config is not sufficient to determine whether the user is logged into ECR public

This PR will decode the expiration timestamp from the authorization string and compare it to the current UTC timestamp.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Author: RedbackThomson

scripts/lib/common.sh

@@ -122,5 +122,21 @@ k8s_controller_gen_version_equals() {
 # fi
 is_public_ecr_logged_in() {
     local public_ecr_url="public.ecr.aws"
-    jq -e --arg url $public_ecr_url '.auths | has($url)' ~/.docker/config.json > /dev/null;
+
+    # Load the auth string
+    # Base64 decode it
+    # Parse it as <Username>:<B64 Payload>, and take only the payload
+    # Base64 decode it
+    # Read the "expiration" value
+    local expiration_time=$(jq -r --arg url $public_ecr_url '.auths[$url].auth' ~/.docker/config.json | base64 -d | cut -d":" -f2 | base64 -d | jq -r ".expiration")
+
+    # If any part of this doesn't exist, the user isn't logged in
+    [ -z "$expiration_time" ] && exit 1
+
+    local current_time=$(date +%s)
+
+    # If the credentials have expired, the user isn't logged in
+    [ "$expiration_time" -lt "$current_time" ] && exit 1
+
+    exit 0
 }