feat: add Google broker configuration profiles

docs/google-idp-brokering.md

@@ -0,0 +1,28 @@
+# Google IdP brokering
+
+Keycloak is the only issuer trusted by AP1–AP4. Google is an upstream Identity
+Provider; applications do not receive or validate a Google token.
+
+## Two verification profiles
+
+The default local profile imports a second Keycloak realm named `mock-google`.
+It acts as a controllable OIDC provider and allows tests to choose claims such
+as a duplicate email, `email_verified=false`, `hd`, and `picture`. This is the
+safe way to reproduce an unsafe email auto-link without impersonating a real
+Google account.
+
+The real-Google profile is configured explicitly:
+
+1. Create a Google OAuth **Web application**.
+2. Register the exact redirect URI printed by
+   `./scripts/configure-google-idp.sh`.
+3. Put `GOOGLE_CLIENT_ID` and `GOOGLE_CLIENT_SECRET` in ignored `.env`.
+4. Start the stack and run the configuration script.
+
+The script writes `providerId=google`, `trustEmail=false`, minimal
+`openid profile email` scopes, and `syncMode=IMPORT` through the Keycloak Admin
+API. Credentials are never written to the realm export or repository.
+
+Google requires a public HTTPS redirect for non-local deployments. Local mock
+verification proves the Keycloak brokering boundary; a real Google login is a
+separate credentialed acceptance profile.