This is a sample Jenkins client code snippet that helps authenticate Jenkins REST API calls by getting crumb from Jenkins's crumbIssuer using valid credentials.

jenkins.py

import os

import requests

class Jenkins:

    def __init__(self):
        self.api_server_url = "your_jenkins_url_goes_here"
        self.username = os.environ["JENKINS_USERNAME"]
        self.password = os.environ["JENKINS_PASSWORD"]
        self.credentials = (self.username, self.password)
        print("Obtaining crumb")
        self.session = requests.Session()
        crumb_response = self.session.get(url="{0:s}/crumbIssuer/api/json".format(self.api_server_url),
                                          auth=self.credentials)
        print("Obtained crumb response: " + crumb_response.text) # for debugging purposes only, remove this line if you do not want the crumb to be printed to console
        cookie = ""
        for key in self.session.cookies.get_dict().keys():
            cookie = key + "=" + self.session.cookies.get_dict()[key]
        self.headers = {crumb_response.json()['crumbRequestField']: crumb_response.json()['crumb'],
                        "Content-Type": "application/json",
                        "Cookie": cookie}