Using simple_salesforce with JWT authentication

simple-salesforce-jwt.py

import jwt
import requests
import datetime
from simple_salesforce import Salesforce
from simple_salesforce.exceptions import SalesforceAuthenticationFailed

def jwt_login(consumer_id, username, private_key, sandbox=False):
    endpoint = 'https://test.salesforce.com' if sandbox is True else 'https://login.salesforce.com'
    jwt_payload = jwt.encode(
        { 
            'exp': datetime.datetime.utcnow() + datetime.timedelta(seconds=30),
            'iss': consumer_id,
            'aud': endpoint,
            'sub': username
        },
        private_key,
        algorithm='RS256'
    )

    result = requests.post(
        endpoint + '/services/oauth2/token',
        data={
            'grant_type': 'urn:ietf:params:oauth:grant-type:jwt-bearer',
            'assertion': jwt_payload
        }
    )
    body = result.json()

    if result.status_code != 200:
        raise SalesforceAuthenticationFailed(body['error'], body['error_description'])
    
    return Salesforce(instance_url=body['instance_url'], session_id=body['access_token'])

what type of key should be the private_key pem?

There's an example in the PyJWT docs (https://pyjwt.readthedocs.io/en/stable/usage.html). It's the textual format in a keyfile as generated by OpenSSL.

How to generate X509 certificate and use that to generate to get JWT token I am having certificate and private key