Hi @cullen - Can you try following ?
--user "tid_<>:_tsec<>"
Note: double quotes around user creds.
also
--aws-sigv4 "aws:amz:auto:s3"
The full cURL should look like this
curl 'https://fly.storage.tigris.dev/mybucket.example.com' \
--aws-sigv4 "aws:amz:auto:s3" \
--user "<tid_>:<tsec_>" \
-X 'PATCH' \
-H 'accept: application/json' \
-H 'content-type: application/json' \
-H 'x-amz-acl: public-read' \
--data-raw '{"cache_control":"","website":{"domain_name":"mybucket.example.com"},"object_regions":"","additional_http_headers":null}'