pip cannot install requirement flask-oidc

The requirement git+https://github.com/schaarj/flask-oidc.git@initial_access_token#egg=flask-oidc fails to install because the themes submodule is added with a git: url instead of https. Git shows the following error:

fatal: remote error: 
  The unauthenticated git protocol on port 9418 is no longer supported.
Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.

@schaarj I guess it's an easy fix in that repository, unless the plan is to switch to authlib anyway.