code: def from_env(cls, reactor=None, env=os.environ):
          
          address = env.get('VAULT_ADDR', 'https://127.0.0.1:8200')
          # This seems to be what the Vault CLI defaults to
          token = env.get('VAULT_TOKEN', 'TEST')
  
          ca_cert = env.get('VAULT_CACERT')
          tls_server_name = env.get('VAULT_TLS_SERVER_NAME')
          client_cert = env.get('VAULT_CLIENT_CERT')
          client_key = env.get('VAULT_CLIENT_KEY')
          cf = ClientPolicyForHTTPS.from_pem_files(
              caKey=ca_cert, privateKey=client_key, certKey=client_cert,
              tls_server_name=tls_server_name
          )
          client, reactor = default_client(reactor, contextFactory=cf)
  
          return cls(address, token, client=client, reactor=reactor)
docs: Create a Vault client with configuration from the environment. Supports
          a limited number of the available config options:
          https://www.vaultproject.io/docs/commands/index.html#environment-variables
          https://github.com/hashicorp/vault/blob/v0.11.3/api/client.go#L28-L40
  
          Supported:
          - ``VAULT_ADDR``
          - ``VAULT_CACERT``
          - ``VAULT_CLIENT_CERT``
          - ``VAULT_CLIENT_KEY``
          - ``VAULT_TLS_SERVER_NAME``
          - ``VAULT_TOKEN``
  
          Not currently supported:
          - ``VAULT_CAPATH``
          - ``VAULT_CLIENT_TIMEOUT``
          - ``VAULT_MAX_RETRIES``
          - ``VAULT_MFA``
          - ``VAULT_RATE_LIMIT``
          - ``VAULT_SKIP_VERIFY``
          - ``VAULT_WRAP_TTL``