Add: Generic OAuth support via well-known

[Philogag]

• Auto detect endpoint by .well-known
• Test passed on authelia

[Philogag]

It will fetch the /.well-known/openid-configuration
And get the authorization_endpoint token_endpoint and userinfo_endpoint

You can get more about the well-known-discovery-endpoints via document of authelia
https://www.authelia.com/integration/openid-connect/introduction/#well-known-discovery-endpoints

Here is my testing config of authelia side

identity_providers:
  oidc:
    clients
      - client_id: 'gerrit'
        client_name: 'Gerrit'
        client_secret: 'xxxxxxxxxxx'
        public: false
        authorization_policy: 'one_factor'
        redirect_uris:
          - 'http://ip_and_port_of_gerrit/oauth'
        scopes:
          - 'openid'
          - 'email'
          - 'profile'
        userinfo_signed_response_alg: 'none'