Unable to add account for Gitea server behind mTLS client auth

[zekecato]

Context:

I have a Gitea server served behind a Caddy reverse proxy with mutual TLS.
When accessing this Gitea instance via the browser I get the usual prompt to select my client certificate.
When accessing this Gitea instance via Git, I have to specify the path to my certificate in .gitconfig like this:

[http https://gitea.domain]
sslCert = CurrentUser\MY\certificate-thumbprint

Problem:

When I go to add my Gitea account to Fork using my personal access token, I get the following error:
Error: The message received was unexpected or badly formatted.

Desired Behaviour:

I am able to add my Gitea account, and Fork presents my client certificate to connect to the server.