Add Azure Blob Storage Adapter

[jopedroliveira]

Add Azure Blob Storage Adapter

This PR adds an Azure Blob Storage adapter to Waffle, following the same structure and conventions as the existing Local and S3 adapters. The intention is to provide native Azure support without altering current behaviour.

Summary

• Implements all Waffle.StorageBehavior callbacks (put/3, url/3, delete/3)
• Direct uploads to Azure Blob Storage via REST API using Shared Key authentication
• Optional SAS-signed URLs for private containers
• Supports public/private containers, multiple containers per definition, and custom blob headers
• Configuration can be fully environment-driven
• Includes documentation and test coverage

New Modules

• lib/waffle/storage/azure.ex — main adapter module
• lib/waffle/storage/azure/uploader.ex — upload logic
• lib/waffle/storage/azure/sas.ex — SAS token generation
• documentation/examples/azure.md — usage guide
• Tests for both the adapter and SAS generator

Updated Files

• Waffle.Definition.Storage — added Azure-related lookups
• mix.exs — optional dependencies (req, timex)
• README.md — new Azure configuration section

Configuration

config :waffle,
  storage: Waffle.Storage.Azure,
  storage_account: {:system, "AZURE_STORAGE_ACCOUNT"},
  container: {:system, "AZURE_STORAGE_CONTAINER"},
  access_key: {:system, "AZURE_ACCESS_KEY"},
  public_access: false,
  expiry_in_minutes: 60

Usage example

defmodule MyApp.Avatar do
  use Waffle.Definition

  def storage_dir(_version, {_, user}) do
    "uploads/users/#{user.id}"
  end

  def azure_blob_headers(_, {file, _}) do
    [content_type: MIME.from_path(file.file_name)]
  end
end

Store

MyApp.Avatar.store({upload, user})

Signed URL

MyApp.Avatar.url({file, user}, signed: true)

Delete

MyApp.Avatar.delete({file, user})

Tests

The PR includes test coverage for:

• Adapter behaviour
• SAS token generation
• Configuration parsing
• Error conditions (missing credentials, unexpected responses, etc.)

Compatibility

• No breaking changes
• Existing adapters remain untouched
• Optional dependencies do not affect users who don’t use Azure

How to Test

export AZURE_STORAGE_ACCOUNT="..."
export AZURE_STORAGE_CONTAINER="..."
export AZURE_ACCESS_KEY="..."

mix test --include azure:true

[Ali-Doggaz]

I am not a maintainer of this project, but just wanted to say that's great, thank you!

[jopedroliveira]

@Ali-Doggaz I created a fork with this in case you need to use that! 💪