Gmail Add-on Development: OAuth 2.0 Implementation Issues and Current Status

Other Questions Gmail
1

I’m working on creating a custom Gmail add-on for our company to handle incoming emails and connect with our internal systems. I’m running into major problems with OAuth 2.0 authentication setup.

The main issues I’m facing:

Authentication Problems:

  • Can’t figure out how to properly implement OAuth 2.0 in the gadget manifest
  • All examples I find still use outdated OpenID authentication
  • OAuth 1.0 is no longer supported but can’t find working OAuth 2.0 examples

Deployment Issues:

  • Google Apps Extensions Console shows OAuth 1.0 deprecation errors
  • New Developer Console doesn’t seem to have deployment options for domain-specific gadgets
  • Getting “Application installation not allowed” messages

What I need help with:

  1. Working manifest.xml example that uses OAuth 2.0 authentication
  2. Step-by-step deployment process for domain-only installation (not marketplace)
  3. How to register OAuth 2.0 credentials with the gadget

Current Setup:

  • Created OAuth 2.0 client credentials in Developer Console
  • Have redirect URL configured: https://mycompany.com/auth/callback
  • Gadget spec file ready but authentication part is broken
<Module>
  <ModulePrefs title="Email Processor">
    <Require feature="gmail" />
    <OAuth2>
      <Service name="emailService">
        <Authorization url="https://accounts.google.com/o/oauth2/auth" />
        <Token url="https://accounts.google.com/o/oauth2/token" />
      </Service>
    </OAuth2>
  </ModulePrefs>
  <Content type="html">
    <script>processIncomingEmail();</script>
  </Content>
</Module>

Is Gmail contextual gadget development still possible? Are there alternative approaches I should consider?

2

gmail gadgets are dead tech - google killed that platform. you’ll wanna switch to google workspace add-ons instead. they use apps script and handle oauth much better. that manifest syntax won’t work anymore. check the workspace add-on quickstart guide - it’ll save you tons of headache vs fighting deprecated apis.

3

It appears you’re facing significant challenges with the deprecated Gmail contextual gadgets which, as you may know, have been obsolete since 2017. The OAuth 2.0 implementation in the gadget manifest has long been problematic, leading many developers to abandon that approach altogether. A more viable solution would be to transition to Google Workspace Add-ons leveraging Apps Script. This modern method not only aligns with current OAuth standards but also offers a robust framework for handling incoming emails and integrating with your internal systems. While it requires some rewrites, especially using the Gmail API directly, this strategic shift can provide a more stable and future-proof solution for your needs.

4

Your OAuth 2.0 setup looks fine structurally, but here’s the real problem: Gmail contextual gadgets have been dead for years. I wasted months trying to get these working back in 2018 before I figured out Google basically abandoned the whole platform. Those “Application installation not allowed” errors you’re getting? That’s because the infrastructure behind these gadgets isn’t maintained anymore. Don’t waste time fighting the old gadget framework. Build a standalone web app that hits the Gmail API directly with proper OAuth 2.0 flows instead. You’ll get the same functionality by having users auth through your web app and processing emails server-side. The Gmail API docs have solid OAuth 2.0 examples that actually work with current Google services.