Bug: updating to v14.0.x yields "invalid peer certificate: UnknownIssuer"

[georglauterbach]

Describe the bug

We're running cargo-deny behind a corporate proxy that does a SSL man-in-the-middle to replace certificates. The certificates are installed in /usr/share/certificates. While v13.9.0 works flawlessly, v14.0.x yields the following error:

[ERROR] failed to fetch advisory database https://github.com/rustsec/advisory-db: An IO error occurred when talking to the server: error sending request for url (https://github.com/rustsec/advisory-db/info/refs?service=git-upload-pack): error trying to connect: invalid peer certificate: UnknownIssuer

We think this may be related to #520.

To reproduce

Run cargo-deny >=v14.0.0 behind a (corporate) proxy that changes certificates.

cargo-deny version

0.14.1

What OS were you running cargo-deny on?

Linux

Additional context

We installed our certificates in the system store via update-ca-certificates.