Change SHA-implementation and make sure signature is correctly generated

start.sh

@@ -12,6 +12,8 @@ fi
 
 set -euo pipefail
 : ${S3_BUCKET_NAME:?"S3_BUCKET_NAME must be set"}
+: ${AWS_REGION:?"AWS_REGION must be set"}
+: ${RETURN_URL:?"RETURN_URL must be set"}
 : ${AWS_ACCESS_KEY_ID:?"AWS_ACCESS_KEY_ID must be set or be possible to fetch from meta-data service on AWS"}
 : ${AWS_SECRET_ACCESS_KEY:?"AWS_ACCESS_KEY_ID must be set or be possible to fetch from meta-data service on AWS"}