Handle OIDC authentication flow via webhook and HTML response

## Quick setup with Keycloak
1. Open your Keycloak
2. Go to `Realm settings` and opn `OpenID Endpoint Configuration`
3. This will opene a new tab. Copy out the `authorization_endpoint`, `token_endpoint` and the `userinfo_endpoint` and add it to the `Set variables` node
4. Go go `Clients` and click `Create client`. In there pick a name of choice.
5. Go to the next step, `Capability config`, disable `Client authentication`. Only `Standard flow` should be checked.
6. Go to the next step `Login settings`. In there copy the Webhook URL of this workflow into the `Valid redirect URIs` field
7. Enter the clientID to the `Set variables` node

Now you can activate the workflow and visit the webhook URL to test. You can find a more detailed setup guid in the description.