Does not support case insensitive headers

[stvhay]

Per RFC, headers are case insensitive: https://www.rfc-editor.org/rfc/rfc2616#section-4.2

Right now, it seems that the extension does not pick up Content-Type and Content-Length headers when they are lower case, as happens when accessing S3 content via AWS cloudfront.

HTTP/2 200
content-type: application/gzip
content-length: 1493671917
date: Tue, 21 Mar 2023 12:05:54 GMT
last-modified: Tue, 21 Mar 2023 10:49:22 GMT
server: AmazonS3