Sign in with Google temporarily disabled for this app - oauth-2.0

Question

We are facing the below screen when trying to authenticate to Google. The app that we are trying to authenticate is used for internal development and we did not publish it to our users.
Any idea why this occurs?
We faced an Unverified App screen before (as below) but now the authentication is disabled.

Answer 1

OAuth Client Verification
Starting July 18, 2017, Google OAuth clients that request certain sensitive OAuth scopes will be subject to review by Google.
OAuth Client Verification
Starting July 18, 2017, Google OAuth clients that request certain sensitive OAuth scopes will be subject to review by Google.
Review is not required if you are only using it under the same account as created the project in Google Developer console. You can read more about this change in this help center article.
This change applies to Google OAuth web clients, including those used by all Apps Script projects. By verifying your app with Google, you can remove the unverified app screen from your authorization flow and give your users confidence that your app is non-malicious.
Once you have applied for verification it takes around a week and it should start working.

Answer 2

I found this thread some time ago when this happened to us in our development project on Google Cloud Platform.
You can use a project for development without verification. No problem on that. But there are some limitations (more information here and here). Basically, we reached the limit of 100 users accessing the application. It was strange because we were testing with few accounts (5-6) until we found that, if you uninstall and install the application again, it counts as a new user. We were testing incremental authorization, so we uninstalled/installed the application a lot of times and we reached the quota.
When you reach this limit, you will see the message "Sign in with Google temporarily disabled for this app" and only users from the organization where the project is hosted can access the application. So we couldn't make test with our accounts from a demo domain or our Gmail accounts.
The only solution available was to pass the OAuth verification form (even if you didn't want to publish the application), but there were problems to do it. For example, it was mandatory to remove http://localhost from valid OAuth URLs. And more problems related with development.
❗ But this has changed recently. I have accessed to OAuth credentials screen in Google Cloud Platform (APIs & Services > Credentials > OAuth consent screen) during this week and now the page it's different. Now you don't need to specify "Authorised JavaScript origins" and "Authorised redirect URIs", you just need to specify your scopes for Google APIs and the Authorised domains. Then, at the bottom of the page you will find the button "Submit Verification" and the process will start. You will also find some information on the right:
About the consent screen
The consent screen tells your users who is requesting access to their data and what kind of data you're asking to
access.
OAuth Developer Verification
To protect you and your users, your
consent screen may need to be verified by Google. Without
verification, your users will see an additional page indicating that
your app is not verified by Google.
Verification is required if
Your application type is public, and You
add a sensitive scope Verification may take several days to complete.
You will receive email updates as it's processed.
Saving without publishing
Even though your consent screen is
unpublished, you can still test your application with users with the
following limitations:
Sensitive scopes are limited to 100 grant requests before verification
is required
Users see an additional page indicating that your app is
not verified by Google.
To include "Authorised Javascript Origins" and Authorised redirect URIs" you need to go to APIs & Services > Credentials and there click on your OAuth 2.0 client ID. There will be a form where you can add them.
In our case it took 1 day to get a response from Google. In the email there were some instructions to pass the verification. We had to reply the email with a video uploaded on YouTube addressing the following points:
How does user sign-up on your app and grants access to the sensitive scopes requested in verification?
OAuth consent screen as seen by end users
How does your application use the requested scopes to provide services to developers?
A test account email and the password for us to test the user sign-up process and validate the project's functionality.
We recorded a video showing points 1, 2 and 3 and sent them a test account for number 4.
After 1 day, we got another response from Google confirming that our project had been verified.
So finally the problem was solved! 🙂
I hope this could help people in the same situation. It was really annoying for us.

Answer 3

I had to go into my Google Apps Script settings and turn on the "Google Apps Script API" setting. Then I tried again, and the script executed correctly without issue.
I had used the script a couple of weeks ago and it worked fine, so something must have happened between then and now that changed it... Not sure what caused that setting to switch.