error.log

2023-11-13T20:45:35.590Z backstage info loaded dynamic backend plugin 'roadiehq-scaffolder-backend-module-utils-dynamic' from 'file:///opt/app-root/src/dynamic-plugins-root/roadiehq-scaffolder-backend-module-utils-dynamic'
Backend failed to start up Error: You must configure at least one key in backend.auth.keys for production.
at ServerTokenManager.fromConfig (/opt/app-root/src/node_modules/@backstage/backend-common/dist/index.cjs.js:4038:13)
at makeCreateEnv (/opt/app-root/src/packages/backend/dist/index.cjs.js:536:57)
at main (/opt/app-root/src/packages/backend/dist/index.cjs.js:613:21)

solution-helm.yaml

# ...
upstream:
  backstage:
    appConfig:
      app:
        baseUrl: 'https://{{- include "janus-idp.hostname" . }}'
      backend:
        auth:
          keys:
            # add a secret
            - secret: <my secret>
# ...

A way to generate a key is using node:

node -p 'require("crypto").randomBytes(24).toString("base64")'