upstream-rocketchat/packages/release-action/src/createNpmFile.ts

import fs from 'node:fs';
import fsPromise from 'node:fs/promises';

import * as core from '@actions/core';

export async function createNpmFile() {
	// With trusted publishing (OIDC) there is no token, and a bogus auth line in .npmrc
	// takes precedence over the OIDC exchange, so leave the file alone.
	if (!process.env.NPM_TOKEN) {
		core.info('No NPM_TOKEN provided, relying on the registry authentication already in place');
		return;
	}

	const userNpmrcPath = `${process.env.HOME}/.npmrc`;

	if (fs.existsSync(userNpmrcPath)) {
		core.info('Found existing user .npmrc file');
		const userNpmrcContent = await fsPromise.readFile(userNpmrcPath, 'utf8');
		const authLine = userNpmrcContent.split('\n').find((line) => {
			// check based on https://github.com/npm/cli/blob/8f8f71e4dd5ee66b3b17888faad5a7bf6c657eed/test/lib/adduser.js#L103-L105
			return /^\s*\/\/registry\.npmjs\.org\/:[_-]authToken=/i.test(line);
		});
		if (authLine) {
			core.info('Found existing auth token for the npm registry in the user .npmrc file');
		} else {
			core.info("Didn't find existing auth token for the npm registry in the user .npmrc file, creating one");
			fs.appendFileSync(userNpmrcPath, `\n//registry.npmjs.org/:_authToken=${process.env.NPM_TOKEN}\n`);
		}
	} else {
		core.info('No user .npmrc file found, creating one');
		fs.writeFileSync(userNpmrcPath, `//registry.npmjs.org/:_authToken=${process.env.NPM_TOKEN}\n`);
	}
}