RUSTSEC-2023-0052: webpki: CPU denial of service in certificate path building

> webpki: CPU denial of service in certificate path building

| Details | |
| ------------------- | ---------------------------------------------- |
| Package | `webpki` |
| Version | `0.21.4` |
| Date | 2023-08-22 |

When this crate is given a pathological certificate chain to validate, it will
spend CPU time exponential with the number of candidate certificates at each
step of path building.

Both TLS clients and TLS servers that accept client certificate are affected.

This was previously reported in
<https://github.com/briansmith/webpki/issues/69> and re-reported recently
by Luke Malinowski.

`rustls-webpki` is a fork of this crate which contains a fix for this issue
and is actively maintained.

See [advisory page](https://rustsec.org/advisories/RUSTSEC-2023-0052.html) for additional details.

Start by checking whether forc uses the affected webpki 0.21.4 dependency, then read the linked RustSec advisory and the rustls-webpki fix. Done means the vulnerable dependency is no longer used and the affected TLS client and client-certificate server paths remain covered by the project’s checks.

Written by the indexing model from the issue text.