ES256 signed PrivateKeyJWT in OAuth2Session

[jordaniversen]

Sorry for my ignorance as I'm new to this. I have a JWK with an EC P-256 key pair, and when I do:

method = PrivateKeyJWT(token_endpoint)
# method.alg = "ES256"
session = OAuth2Session(client_id, private_jwk, token_endpoint_auth_method=method, scope=scopes)
token = session.fetch_token(token_endpoint)

I get the error:

@classmethod
def check_required_fields(cls, data):
    for k in cls.REQUIRED_JSON_FIELDS:
        if k not in data:
            raise ValueError('Missing required field: "{}"'.format(k))
E  ValueError: Missing required field: "e"

..\venv\lib\site-packages\authlib\jose\rfc7517\models.py:120: ValueError

When I uncomment the method.alg = "ES256" line, then it works. Should the library be detecting the type of key, and overriding the default of "RS256"? I assume a particular type of private JWK can only be used with a particular signing algorithm.

I'm using v0.15.5. Thank you