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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def create_jwt_token(secret, client_id):
 """ Create JWT token for GOV.UK Notify Tokens have standard header: { "typ": "JWT", "alg": "HS256" } Claims consist of: iss: identifier for the client iat: issued at in epoch seconds (UTC) :param secret: Application signing secret :param client_id: Identifier for the client :return: JWT token for this request """

    assert secret, "Missing secret key"
    assert client_id, "Missing client id"

    headers = {
        "typ": __type__,
        "alg": __algorithm__
    }

    claims = {
        'iss': client_id,
        'iat': epoch_seconds()
    }

    return jwt.encode(payload=claims, key=secret, headers=headers).decode()