Add GitlabAuth & ForgejoAuth providers & make tokens storage modular

[brenard]

Hello,

In a new project, I need to handle Gitlab OAuth2 from CLI and I was happy to find your lib. I add support for Gitlab that does not support urn:ietf:wg:oauth:2.0:oob redirect URI so I also add a redirect_uri parameter to AuthFlow.auth_code().

Furthermore, I don't want to store tokens in my case and I think it's could be great to have possibilty to store tokens in a more secure way. So, I create a modular way to store token: I keep your method as default and adding two new storage backends:

• NoneStorage: disable storage
• KeryingStorage: use keyring lib to store token

To use one of them, we just have to provide one instance of them by using the tokens_storage parameter of the provider:

auth = GitlabAuth(
    client_id,
    secret_id,
    ['read_user'],
    url=server_url,
    tokens_storage=KeyringStorage() ,
)

The storage backend constructor allow to customize their behaviour, so I add some parameters:

• a path parameter to ConfigFileStorage to change the default storage path (~/.config/PythonCliAuth/tokens.json)
• a service_name parameter to KeyringStorage to change the default service name (python-cli-oauth2)

Edit: I also added Forgejo auth provider too. It may be also compatible with Gitea.