Add auth support (#21)

* Updates

* Update

* Update

* Update

* Update

* Yarn sometimes prefers npmrc, so use same token

* Description

* Update readme

* Feedback

* Add type

* new toolkit and scoped registries

* npmrc in RUNNER_TEMP

* Dont always auth

* Try exporting blank token

* Get auth working for now pending runner changes

* Fix string interpolation for auth token.

* Don't export both userconfigs

* Update authutil.js

* Add single quotes for authString

* Fix the registry string.

* Use userconfig and append trailing slash

* Keep in root of repo

* Try just adding auth token

* Remove auth token

* Try changes again

* Add tests

* Npm and GPR samples

* Add types

__tests__/authutil.test.ts

@@ -0,0 +1,62 @@
+import io = require('@actions/io');
+import fs = require('fs');
+import path = require('path');
+
+const tempDir = path.join(
+  __dirname,
+  'runner',
+  path.join(
+    Math.random()
+      .toString(36)
+      .substring(7)
+  ),
+  'temp'
+);
+
+const rcFile = path.join(tempDir, '.npmrc');
+
+process.env['GITHUB_REPOSITORY'] = 'owner/repo';
+process.env['RUNNER_TEMP'] = tempDir;
+import * as auth from '../src/authutil';
+
+describe('installer tests', () => {
+  beforeAll(async () => {
+    await io.rmRF(tempDir);
+    await io.mkdirP(tempDir);
+  }, 100000);
+
+  beforeEach(() => {
+    if (fs.existsSync(rcFile)) {
+      fs.unlinkSync(rcFile);
+    }
+    process.env['INPUT_SCOPE'] = '';
+  });
+
+  it('Sets up npmrc for npmjs', async () => {
+    await auth.configAuthentication('https://registry.npmjs.org/');
+    expect(fs.existsSync(rcFile)).toBe(true);
+    expect(fs.readFileSync(rcFile, {encoding: 'utf8'})).toMatchSnapshot();
+  });
+
+  it('Appends trailing slash to registry', async () => {
+    await auth.configAuthentication('https://registry.npmjs.org');
+
+    expect(fs.existsSync(rcFile)).toBe(true);
+    expect(fs.readFileSync(rcFile, {encoding: 'utf8'})).toMatchSnapshot();
+  });
+
+  it('Configures scoped npm registries', async () => {
+    process.env['INPUT_SCOPE'] = 'myScope';
+    await auth.configAuthentication('https://registry.npmjs.org');
+
+    expect(fs.existsSync(rcFile)).toBe(true);
+    expect(fs.readFileSync(rcFile, {encoding: 'utf8'})).toMatchSnapshot();
+  });
+
+  it('Automatically configures GPR scope', async () => {
+    await auth.configAuthentication('npm.pkg.github.com');
+
+    expect(fs.existsSync(rcFile)).toBe(true);
+    expect(fs.readFileSync(rcFile, {encoding: 'utf8'})).toMatchSnapshot();
+  });
+});