Automated Let's Encrypt certificate generator on Azure Functions for App Services

Useful for App Services based on Container / Docker

Setup

create Azure Function App (with Hosting Plan: Consumption)
in Azure Function App add:
- Application settings:
  - WEBSITE_NODE_DEFAULT_VERSION = 8.10.0
  - OPENSSL_PATH = D:\Program Files (x86)\Git\usr\bin\openssl.exe
  - TEST = false
- Connection strings (with type Custom):
  - CLIENT_ID = How to get client id & secret »
  - CLIENT_SECRET = How to get client id & secret »
  - SUBSCRIPTION_ID = Azure AD > Subscriptions > Subscription ID
  - TENANT = Azure AD > Azure Active Directory > Properties > Directory ID
  - PFX_PASSWORD = Random password
  - AZURE_STORAGE_CONNECTION_STRING = Connection string to any storage for Let's Encrypt challenges
  - AZURE_STORAGE_CONTAINER = Container name in storage for Let's Encrypt challenges
in Azure Function App create function from template: Timer trigger / Javascript (named: TimerTriggerJS1)
copy wwwroot to Azure Function App wwwroot
run npm install in wwwroot
change parameters in file index.js for your App Service
in your app add redirect from path /.well-known/acme-challenge/:key to https://«storage_name».blob.core.windows.net/«storage_container»/:key (example for: expressjs)
run TimerTriggerJS1 function