Hi,

I will add to the previous message that if you want to specify a non-default region, the environment variable you're looking for is probably AWS_REGION (or AWS_DEFAULT_REGION starting with GDAL 2.3), rather than AWS_S3_ENDPOINT (see https://gdal.org/user/virtual_file_systems.html#vsis3-aws-s3-files-random-reading)

Also, I have successfully used rasterio on private AWS S3 buckets without having to touch any environment variable, so unless I incorrectly understand your case, any extra configuration should not be necessary.

Best,

Guillaume Lostis