Openconnect-sso

- Updating `poetry2nix` to fix build on `nixpkgs-unstable`
([issues/40](https://github.com/vlaci/openconnect-sso/issues/40),
[pull/41](https://github.com/vlaci/openconnect-sso/pull/41))
- Relax `structlog`'s version restriction
([pull/44](https://github.com/vlaci/openconnect-sso/pull/44))

- Updating dependencies to newer versions
- `python-keyring` is updated to 22.0.1 to fix Arch Linux (AUR) packaging

- Use "modern" style authentication header
([pull/37](https://github.com/vlaci/openconnect-sso/pull/37))

It is inspired by
[openconnect/mr/75](https://gitlab.com/openconnect/openconnect/-/merge_requests/75)
Without this header recent AnyConnect servers will not send the correct
reply redirecting to the authentication page

New features

- New `--on-disconnect` argument to run shell command when `openconnect` exits
([pull/33](https://github.com/vlaci/openconnect-sso/pull/33))

It is useful for example to restart SSH Control Master connections upon exit.

- Adding `--proxy` argument from OpenConnect
([pull/20](https://github.com/vlaci/openconnect-sso/pull/20))

Authentication honors this argument too

- Experimental Windows support
([pull/16](https://github.com/vlaci/openconnect-sso/pull/16))

`sudo` binary needs to be installed in addition to `openconnect`

Bug fixes

- Application no longer crashes when the config file is not readable
([pull/33](https://github.com/vlaci/openconnect-sso/pull/33))
- Work around issue with password retrieval from `kwallet`
([pull/26](https://github.com/vlaci/openconnect-sso/pull/26))

New Features

- Adding `--authgroup` argument from OpenConnect

Some VPN endpoints require users to post a valid authgroup (in
OpenConnect lingua) as part of the `group-access` xml node. Up until
now it was only possilbe to override the authgroup from the
configuration or from an AnyConnect XML profile.

Other Notes

- Removed max version constraint from `attrs` and update dependencies.
It works with a more recent version after the `convert=` deprecation
issues had been resolved for the previous upgrade.

Prelude

It is now possible to install `openconnect-sso` using a systemwide
installation of `Qt` by declaring dependencies to `PyQt5` and
`PyQtWebEngine` optional.

New Features

- `--authenticate [json|shell]` command line a Change