refer to the session secret using the application name prefix

kustomize/app/deployment.yaml

@@ -22,7 +22,7 @@ spec:
             - name: sinatra-web
               containerPort: 4567
           env:
-            - name: SESSION_SECRET
+            - name: KUBERNAUT_SESSION_SECRET
               valueFrom:
                 secretKeyRef:
                   name: kubernaut

lib/config.rb

@@ -12,7 +12,7 @@ class Config
     @prefix = prefix
     @cat = cat
 
-    session_secret ||= ENV.fetch "SESSION_SECRET" do
+    session_secret ||= fetch_env "SESSION_SECRET" do
       SecureRandom.hex SESSION_SECRET_HEX_LENGTH
     end