Make config more docker friendly

dev/docker/docker-compose-arm64.yml

@@ -44,6 +44,8 @@ services:
     restart: on-failure
     depends_on:
       - keycloak
+    environment:
+      RDPGW_SERVER__SESSION_STORE: file
     healthcheck:
       test: ["CMD", "curl", "-f", "http://keycloak:8080"]
       interval: 30s

dev/docker/docker-readme.md

@@ -0,0 +1,36 @@
+# RDPGW
+## What is RDPGW?
+Remote Desktop Gateway (RDPGW, RDG or RD Gateway) provides a secure encrypted connection 
+to user desktops via RDP. It enhances control by removing all remote user direct access to 
+your system and replaces it with a point-to-point remote desktop connection.
+
+## How to use this image
+The remote desktop gateway relies on an OpenID Connect authentication service, such as Keycloak, 
+Azure AD or Google, and a backend remote desktop service such as XRDP, gnome-remote-desktop, or
+Windows VMs. Make sure that these services have been properly setup and can be reached from
+where you will run this image. 
+
+This image works stateless, which means it does not store any state by default. In case you configure
+the session store to be a `filestore` a little bit of session information is stored temporarily. This means
+that a load balancer would need to maintain state for a while, which typically is the case.
+
+Session and token encryption keys will be randomized on startup. As a consequence sessions will be
+invalidated on restarts and if you are load balancing the different instances will not be able to share
+user sessions. Make sure to set these encryption keys to something static, so they can be shared 
+across the different instances if this is not what you want.
+
+## Configuration through environment variables
+```bash
+docker --run name rdpgw bolkedebruin/rdpgw:latest \
+  -e RDPGW_SERVER__SSL_CERT_FILE=/etc/rdpgw/cert.pem
+  -e RDPGW_SERVER__SSL_KEY_FILE=/etc/rdpgw.cert.pem
+  -e SSL_KEY=<SSL_KEY>
+  -e RDPGW_SERVER__GATEWAY_ADDRESS=https://localhost:443
+  -e RDPGW_SERVER__SESSION_KEY=thisisasessionkeyreplacethisjetz  # 32 characters
+  -e RDPGW_SERVER__SESSION_ENCRYPTION_KEY=thisisasessionkeyreplacethisnunu # 32 characters
+  -e RDPGW_OPENID__PROVIDER_URL=http://keycloak:8080/auth/realms/rdpgw
+  -e RDPGW_OPENID__CLIENT_ID=rdpgw
+  -e RDPGW_OPENID__CLIENT_SECRET=01cd304c-6f43-4480-9479-618eb6fd578f
+  -e RDPGW_SECURITY__SECURITY_PAA_TOKEN_SIGNING_KEY=prettypleasereplacemeinproductio # 32 characters
+  -v conf:/etc/rdpgw
+```