add env_file for local vars in docker-compose

docker-compose.yml

@@ -10,12 +10,10 @@ services:
     ports:
       - "3000:3000"
     environment:
-      - SESSION_SECRET=CHANGE ME TO RANDOM VALUE
       - REDIS_HOST=redis://redis
       - DATABASE_URL=postgres://postgres@postgres/canvas
-      - AUTH_ENDPOINT=https://auth.fediverse.events
-      - AUTH_CLIENT=canvas
-      - AUTH_SECRET=${AUTH_SECRET}
+    env_file:
+      - .env.local
     depends_on:
       redis:
         condition: service_healthy