Make a web app accessible to external (existing) Google accounts

[Froogle]

Dear Google community,

I have created a SAML application (web app) on admin.google.com.
It is a firewall login.
Now I want a group to have access that also contains external users.
Unfortunately this only seems to work for the internal users, although I can select the created group in the SAML app.
The external users always get the error:

403. That's an error.

Error: app_not_configured_for_user

Service is not configured for this user.

Is it even possible to make an app accessible to external users which was created at

admin.google.com -> Apps -> Web- and mobile Apps

And if not, is there another way to create a SAML app?

Many thanks in advance!

[cryptochrome]

I don't think it's possible to authenticate external users to your internal apps. Users you want to authenticate using SAML have to exist in your directory. You could try using Google Cloud Identity (there is a free edition) and hand out user accounts to external parties, so they can authenticate against your directory. 

If you want external users from other directories to authenticate against your app, you will probably have to move the entire thing to Google Cloud, where you have way more options (like directory federation, OAuth with personal Google accounts, etc.). 

Or you build some kind of ZTNA infrastructure with products like Permiter 81 or Cloudflare Access. 

Just some wild guesses 🙂