A Datasette plugin in a gist - see https://simonwillison.net/2022/Apr/24/pip-install-github/

datasette_expose_some_environment_variables.py

from datasette import hookimpl
from datasette.utils.asgi import Response
import os

REDACT = {"GPG_KEY"}


async def env(request):
    output = []
    for key, value in os.environ.items():
        if key not in REDACT:
            output.append("{}={}".format(key, value))
    return Response.text("\n".join(output))


@hookimpl
def register_routes():
    return [
        (r"^/-/env$", env)
    ]

setup.py

from setuptools import setup

VERSION = "0.1"

setup(
    name="datasette-expose-some-environment-variables",
    description="Expose environment variables in Datasette at /-/env",
    author="Simon Willison",
    license="Apache License, Version 2.0",
    version=VERSION,
    py_modules=["datasette_expose_some_environment_variables"],
    entry_points={
        "datasette": [
            "expose_some_environment_variables = datasette_expose_some_environment_variables"
        ]
    },
    install_requires=["datasette"],
)

You can install this plugin with:

datasette install https://gist.github.com/simonw/b6dbb230d755c33490087581821d7082/archive/872818f6b928d9393737eee541c3c76d6aa4b1ba.zip

I turned this into a released plugin: https://github.com/simonw/datasette-unsafe-expose-env and https://pypi.org/project/datasette-unsafe-expose-env/