After much experimentation I finally found how to do it. What I needed was to pass user name and password to my script in order to allow the code to log into a test server. My test looked like this:
my_module_test.py

import pytest
import my_module

def login_test(username, password):
    instance = my_module.Login(username, password)
    # ...more...

conftest.py

import pytest

def pytest_addoption(parser):
    parser.addoption('--username', action='store', help='Repository user')
    parser.addoption('--password', action='store', help='Repository password')

def pytest_generate_tests(metafunc):
    username = metafunc.config.option.username
    if 'username' in metafunc.fixturenames and username is not None:
        metafunc.parametrize('username', [username])

    password = metafunc.config.option.password
    if 'password' in metafunc.fixturenames and password is not None:
        metafunc.parametrize('password', [password])

Then in my settings file I can use:
.vscode/settings.json

{
    // ...more...
    "python.testing.autoTestDiscoverOnSaveEnabled": true,
    "python.testing.unittestEnabled": false,
    "python.testing.nosetestsEnabled": false,
    "python.testing.pytestEnabled": true,
    "python.testing.pytestArgs": [
        "--exitfirst",
        "--verbose",
        "test/",
        "--username=myname",
        "--password=secret",
    // ...more...
    ],
}

An alternative way is to use pytest.ini file instead:
pytest.ini

[pytest]
junit_family=legacy
addopts = --username=myname --password=secret

Use the pytest_addoption hook function in conftest.py to define a new option.
Then use pytestconfig fixture in a fixture of your own to grab the name.
You can also use pytestconfig from a test to avoid having to write your own fixture, but I think having the option have it's own name is a bit cleaner.

# conftest.py

def pytest_addoption(parser):
    parser.addoption("--name", action="store", default="default name")

# test_param.py 

import pytest

@pytest.fixture(scope="session")
def name(pytestconfig):
    return pytestconfig.getoption("name")

def test_print_name(name):
        print(f"\ncommand line param (name): {name}")

def test_print_name_2(pytestconfig):
    print(f"test_print_name_2(name): {pytestconfig.getoption('name')}")

# in action

$ pytest -q -s --name Brian test_param.py

test_print_name(name): Brian
.test_print_name_2(name): Brian
.