The script uses the Python Requests library to authenticate with Cisco APIC-EM.

1. Username: The prompt specifies the user is devnetuser, which must be assigned as the value for the 'username' key in the payload dictionary.
2. Request Method: The variable response is assigned the result of a POST request. In the requests library, the syntax is requests.post().
3. Headers Argument: The function call includes headers=, which requires the variable name where the HTTP headers are defined. In line 6, the variable is explicitly named header = {'Content-type': 'application/json'}. Therefore, header must be passed to the headers parameter.

Cisco DevNet Documentation: APIC-EM REST API Guide, Section: "Authentication and Security - Getting a Service Ticket."

Cisco Learning Network: Programming for Network Engineers (PRNE), Module 4: "Using REST APIs with Python," Section 4.2 (HTTP Methods and the Requests Library).

Python Requests Documentation: Quickstart Guide - Make a Request, Section: "Passing Parameters In URLs" and "More complicated POST requests." (https://requests.readthedocs.io/en/latest/user/quickstart/)

Cisco Press: Cisco Certified DevNet Associate DEVASC 200-901 Official Cert Guide, Chapter 14: "Cisco Platforms and Development," Subsection: "APIC-EM API Authentication."