Create Keycloak documentation page

Add Keycloak documentation with usage instructions.

Author: monodot

_articles/keycloak.md

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+---
+layout: page
+title: Keycloak
+---
+
+## Cookbook
+
+### Evaluate scopes and view a generated access token
+
+Go to Clients -> (client name) -> Client scopes -> Evaluate.
+
+This allows you to see **protocol mappers** in action and see what a generated access token will look like with the current settings.
+
+This is very useful when integrating other apps with Keycloak, to see what data will be shared with the third party app.