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

node_modules/isexe/index.js

@@ -0,0 +1,57 @@
+var fs = require('fs')
+var core
+if (process.platform === 'win32' || global.TESTING_WINDOWS) {
+  core = require('./windows.js')
+} else {
+  core = require('./mode.js')
+}
+
+module.exports = isexe
+isexe.sync = sync
+
+function isexe (path, options, cb) {
+  if (typeof options === 'function') {
+    cb = options
+    options = {}
+  }
+
+  if (!cb) {
+    if (typeof Promise !== 'function') {
+      throw new TypeError('callback not provided')
+    }
+
+    return new Promise(function (resolve, reject) {
+      isexe(path, options || {}, function (er, is) {
+        if (er) {
+          reject(er)
+        } else {
+          resolve(is)
+        }
+      })
+    })
+  }
+
+  core(path, options || {}, function (er, is) {
+    // ignore EACCES because that just means we aren't allowed to run it
+    if (er) {
+      if (er.code === 'EACCES' || options && options.ignoreErrors) {
+        er = null
+        is = false
+      }
+    }
+    cb(er, is)
+  })
+}
+
+function sync (path, options) {
+  // my kingdom for a filtered catch
+  try {
+    return core.sync(path, options || {})
+  } catch (er) {
+    if (options && options.ignoreErrors || er.code === 'EACCES') {
+      return false
+    } else {
+      throw er
+    }
+  }
+}