The token is not yet valid (iat) aka add leeway config

[tonkolviktor]

Hi Brian,

thanks for the project, it's great!!!!

In our setup unfortunately the clocks are not 100% synchronized as it turns out :)
Our KeyCloak is 0.5s in the future to our client application, this is a problem for PyJWT specially since version 2.6.0: jpadilla/pyjwt#824

File "/usr/local/lib/python3.10/dist-packages/jwt/api_jwt.py", line 210, in decode
    decoded = self.decode_complete(
  File "/usr/local/lib/python3.10/dist-packages/jwt/api_jwt.py", line 162, in decode_complete
    self._validate_claims(
  File "/usr/local/lib/python3.10/dist-packages/jwt/api_jwt.py", line 242, in _validate_claims
    self._validate_iat(payload, now, leeway)
  File "/usr/local/lib/python3.10/dist-packages/jwt/api_jwt.py", line 280, in _validate_iat
    raise ImmatureSignatureError("The token is not yet valid (iat)")
jwt.exceptions.ImmatureSignatureError: The token is not yet valid (iat)

I'm preparing a fix, but I do not understand something, which is also related to: #2

Why do you have 'jwt' in install_requires and not PyJWT, the code seem to use jwt.PyJWKClient which is AFAIK only available in PyJWT?