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Basically the issue was with my application configuration, not the reverse proxy it self.
When using transparent, various information is forwarded. According to the Caddy docs transparent is shorthand for various upstream headers.
However, my application had to be aware of that. This is doable (using yml config) as follows by adding this to the configuration:
server:
use-forward-headers: true
tomcat:
remote-ip-header: X-Forwarded-For
protocol-header: X-Forwarded-Proto
internal-proxies: 192\.168\.\d{1,3}\.\d{1,3}
protocol-header-https-value: https
Source:stackexchange.com