Add sample for Onshape (#377)

* Add sample for Onshape

* Make getService private

Author: AlnisS

samples/Onshape.gs

@@ -0,0 +1,81 @@
+/*
+ * This sample demonstrates how to configure the library for the Onshape API.
+ * To generate OAuth credentials, create an OAuth application here:
+ * https://dev-portal.onshape.com/
+ */
+
+// Make sure to include any trailng '=' symbols in the ID and Secret.
+var CLIENT_ID = '...';
+var CLIENT_SECRET = '...';
+
+/**
+ * Authorizes and makes a request to the Onshape API.
+ */
+function run() {
+  var service = getService_();
+  if (service.hasAccess()) {
+    // Make a request to retrieve a list of the user's documents.
+    // This requires enabling the OAuth2Read scope for the application in the
+    // Onshape developer portal. ("Application can read your documents")
+    var url = 'https://cad.onshape.com/api/documents';
+    var response = UrlFetchApp.fetch(url, {
+      headers: {
+        Authorization: 'Bearer ' + service.getAccessToken()
+      }
+    });
+    var result = JSON.parse(response.getContentText());
+    Logger.log(JSON.stringify(result, null, 2));
+  } else { 
+    var authorizationUrl = service.getAuthorizationUrl();
+    Logger.log('Open the following URL and re-run the script: %s',
+        authorizationUrl);
+  }
+}
+
+/**
+ * Reset the authorization state, so that it can be re-tested.
+ */
+function reset() {
+  getService_().reset();
+}
+
+/**
+ * Configures the service.
+ */
+function getService_() {
+  return OAuth2.createService('Onshape')
+      // Set the Onshape OAuth endpoint URLs.
+      .setAuthorizationBaseUrl('https://oauth.onshape.com/oauth/authorize')
+      .setTokenUrl('https://oauth.onshape.com/oauth/token')
+
+      // Set the client ID and secret.
+      .setClientId(CLIENT_ID)
+      .setClientSecret(CLIENT_SECRET)
+
+      // Set the name of the callback function that should be invoked to
+      // complete the OAuth flow.
+      .setCallbackFunction('authCallback')
+
+      // Set the property store where authorized tokens should be persisted.
+      .setPropertyStore(PropertiesService.getUserProperties());
+}
+
+/**
+ * Handles the OAuth callback.
+ */
+function authCallback(request) {
+  var service = getService_();
+  var authorized = service.handleCallback(request);
+  if (authorized) {
+    return HtmlService.createHtmlOutput('Success!');
+  } else {
+    return HtmlService.createHtmlOutput('Denied.');
+  }
+}
+
+/**
+ * Logs the redict URI to register.
+ */
+function logRedirectUri() {
+  Logger.log(OAuth2.getRedirectUri());
+}