> ## Documentation Index
> Fetch the complete documentation index at: https://docs.webapp.io/llms.txt
> Use this file to discover all available pages before exploring further.

# OAuth

> Logging in with external sites

OAuth is what lets you log in to a service with an existing Google or Facebook
account.

Webapp.io customers often need to set a redirect target from their "test app" on
an external service to allow logging in to their own accounts.

For this use case, we've created the `layer-oauth-target.cidemo.co` endpoint,
and the flow looks like this:

1. User visits `abcd.cidemo.co`
2. User clicks "log in with Google"
3. User is redirected to a Google login page for a test application
4. The "redirect URI" for that login page is "layer-oauth-target.cidemo.co", so
   the user is sent to `layer-oauth-target.cidemo.co/oauth/login?code=hello`
5. `layer-oauth-target.cidemo.co` reads a cookie to see which cidemo site the
   user was last on, so the user is redirected back to
   `abcd.cidemo.co/oauth/login?code=hello`
6. The application can now read the code and log the user in as usual.

### Combining with white-labeled sites (routing)

The same can be done for layer-oauth-target.demo.example.com, in the case where
a route with `$branch.demo.example.com` exists.