venv/lib/python3.11/site-packages/authlib/oauth2/rfc7523/assertion.py

import time
from authlib.jose import jwt
from authlib.common.security import generate_token


def sign_jwt_bearer_assertion(
        key, issuer, audience, subject=None, issued_at=None,
        expires_at=None, claims=None, header=None, **kwargs):

    if header is None:
        header = {}
    alg = kwargs.pop('alg', None)
    if alg:
        header['alg'] = alg
    if 'alg' not in header:
        raise ValueError('Missing "alg" in header')

    payload = {'iss': issuer, 'aud': audience}

    # subject is not required in Google service
    if subject:
        payload['sub'] = subject

    if not issued_at:
        issued_at = int(time.time())

    expires_in = kwargs.pop('expires_in', 3600)
    if not expires_at:
        expires_at = issued_at + expires_in

    payload['iat'] = issued_at
    payload['exp'] = expires_at

    if claims:
        payload.update(claims)

    return jwt.encode(header, payload, key)


def client_secret_jwt_sign(client_secret, client_id, token_endpoint, alg='HS256',
                           claims=None, **kwargs):
    return _sign(client_secret, client_id, token_endpoint, alg, claims, **kwargs)


def private_key_jwt_sign(private_key, client_id, token_endpoint, alg='RS256',
                         claims=None, **kwargs):
    return _sign(private_key, client_id, token_endpoint, alg, claims, **kwargs)


def _sign(key, client_id, token_endpoint, alg, claims=None, **kwargs):
    # REQUIRED. Issuer. This MUST contain the client_id of the OAuth Client.
    issuer = client_id
    # REQUIRED. Subject. This MUST contain the client_id of the OAuth Client.
    subject = client_id
    # The Audience SHOULD be the URL of the Authorization Server's Token Endpoint.
    audience = token_endpoint

    # jti is required
    if claims is None:
        claims = {}
    if 'jti' not in claims:
        claims['jti'] = generate_token(36)

    return sign_jwt_bearer_assertion(
        key=key, issuer=issuer, audience=audience, subject=subject,
        claims=claims, alg=alg, **kwargs)