[Unity] Build Asset Bundle, and upload to AWS-S3

UnityAssetBundleBuilder.cs

using UnityEngine;
using UnityEngine.Networking;
using UnityEditor;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using System.Text;
using System;


// Usage
// 1. Put this script to Assets/Editor/
// 2. Execute [Menu] -> [Build] -> [Build Asset Bundle]
public class UnityAssetBundleBuilder {

	// Enter your s3 informations
	private const string s3Bucket = "";
	private const string s3KeyBase = "";
	private const string s3AccessKeyId = "";
	private const string s3SecretAccessKey = "";

	private const string baseDir = "AssetBundles";
	private const string s3PostUrl = "http://" + s3Bucket + ".s3.amazonaws.com/";

	private static readonly BuildTarget[] buildTargets =
		new BuildTarget[] { BuildTarget.iOS, BuildTarget.Android };

	private static readonly Dictionary<string, string> postParams = new Dictionary<string, string> {
		{ "acl", "public-read" },
		{ "Content-Type", "application/octet-stream" },
		{ "x-amz-meta-uuid", "14365123651274" },
		{ "AWSAccessKeyId", s3AccessKeyId },
	};

	private const string policyBase = "{{" +
		"\"expiration\": \"{0}\"," +
		"\"conditions\": [" +
		"    {{\"bucket\": \"" + s3Bucket + "\"}}," +
		"    [\"starts-with\", \"$key\", \"{1}\"]," +
		"    {{\"acl\": \"public-read\"}}," +
		"    [\"starts-with\", \"$Content-Type\", \"application/octet-stream\"]," +
		"    {{\"x-amz-meta-uuid\": \"14365123651274\"}}" +
		"  ]" +
		"}}";


	[MenuItem("Build/Build AssetBundles")]
	public static void Build() {
		if (Directory.Exists(baseDir)) {
			Directory.Delete(baseDir, true);
		}
		Directory.CreateDirectory(baseDir);

		foreach (BuildTarget target in buildTargets) {
			buildForPlatform(target);
		}
	}

	private static void buildForPlatform(BuildTarget target) {
		var platform = target.ToString().ToLower();
		string dir = Path.Combine(baseDir, platform);
		Directory.CreateDirectory(dir);

		BuildPipeline.BuildAssetBundles(dir,
		                                BuildAssetBundleOptions.ChunkBasedCompression,
		                                target);

		var dirInfo = new DirectoryInfo(dir);
		foreach (var fileInfo in dirInfo.GetFiles()) {
			Debug.Log("upload : " + fileInfo.FullName);
			uploadToS3(platform, fileInfo);
		}
	}

	private static void uploadToS3(string platform, FileInfo fileInfo) {

		var form = new WWWForm();
		foreach (KeyValuePair<string, string> pair in postParams) {
			form.AddField(pair.Key, pair.Value);
		}

		string s3Key = Path.Combine(s3KeyBase, platform + "/" + fileInfo.Name);
		form.AddField("key", s3Key);

		string expiration = DateTime.Now.AddMinutes(1).ToString("yyyy-MM-ddTHH:mm:ss.fffZ");
		string policy = string.Format(policyBase, expiration, s3Key);
		string base64Policy = Convert.ToBase64String(Encoding.UTF8.GetBytes(policy));

		var hmac = new HMACSHA1(Encoding.UTF8.GetBytes(s3SecretAccessKey));
		string signature = Convert.ToBase64String(hmac.ComputeHash(Encoding.UTF8.GetBytes(base64Policy)));

		form.AddField("Policy", base64Policy);
		form.AddField("Signature", signature);

		byte[] fileBytes = File.ReadAllBytes(fileInfo.FullName);
		form.AddBinaryData("file", fileBytes, fileInfo.Name, "application/octet-stream");

		if (!postRequestWithRetry(s3Key, form)) {
			Debug.LogError("Upload failed : " + s3Key);
		}
	}

	private static bool postRequestWithRetry(string s3Key, WWWForm form, int retryLimit = 5) {
		for (int i = 0; i < retryLimit; i++) {
			if (postRequest(s3Key, form)) {
				return true;
			}
			Debug.Log("Retry : " + (i + 1));
		}
		return false;
	}

	private static bool postRequest(string s3Key, WWWForm form) {
		using (UnityWebRequest www = UnityWebRequest.Post(s3PostUrl, form)) {
			var s = www.Send();
			long startTick = DateTime.Now.Ticks;
			while (!s.isDone) {
				if (DateTime.Now.Ticks > startTick + 10L * 10000000L) {
					Debug.LogWarning("Timeout");
					break;
				}
			}

			if (string.IsNullOrEmpty(www.error)) {
				Debug.Log("Uploaded : " + s3PostUrl + s3Key);
				return true;

			} else {
				Debug.LogWarning("Error : " + www.error);
				return false;
			}
		}
	}

}

Can you tell me if this script can be used as a Post Process Build Script in Unity Cloud Build?
If so is the baseDir going to be different?

In this doc: https://docs.unity3d.com/Manual/UnityCloudBuildAddressables.html
It says:

The Addressable content for your build is located at $WORKSPACE/.build/last/<BUILD_TARGET_ID>/extra_data/addrs/

Can I access the $WORKSPACE variable to get the root path?

Thanks in advance