[fastlane] Fix S3ClientHelper side effects (#16687)

* Updates S3ClientHelper to prevent side effects

The initializer was calling Aws.config.update which was overwriting
existing configuration. This was preventing access when using
STS/Aws::AssumeRoleCredentials to assume a temporary IAM role.

Removing the need to initialize with access_key/secret allows the caller
to update Aws.config before calling fastlane and having their expected
credentials used. Credentials will now be pulled from Amazon's
documented sources.

Maintains `region` option by initializing the S3 client with this
option.

* Updates match's S3Storage object to initialize S3ClientHelper with new
interface.

* Updates S3ClientHelper with option s3_client initializer option

This is mainly to be used to inject this dependency in for specs, but if
callers feel they would rather configure an s3 client this allows them
to do so.

* Updates S3ClientHelper with much more versatile initializer

Reverts changes to keep initializer interface non-breaking.
Updates creation of underlying S3 client to support passed in
credentials (access_key/secret). Will use AWS config otherwise

* Reverts change in S3Storage that prevented access_key/secret from being
used if passed in

fastlane/lib/fastlane/helper/s3_client_helper.rb

@@ -3,14 +3,15 @@
 module Fastlane
   module Helper
     class S3ClientHelper
-      attr_reader :client
+      attr_reader :access_key
+      attr_reader :region
 
-      def initialize(access_key: nil, secret_access_key: nil, region: nil)
-        creds = Aws::Credentials.new(access_key, secret_access_key)
-        Aws.config.update(
-          region: region,
-          credentials: creds
-        )
+      def initialize(access_key: nil, secret_access_key: nil, region: nil, s3_client: nil)
+        @access_key = access_key
+        @secret_access_key = secret_access_key
+        @region = region
+
+        @client = s3_client
       end
 
       def list_buckets
@@ -50,12 +51,28 @@ def find_bucket!(bucket_name)
 
         return bucket
       end
-    end
 
-    private
+      private
+
+      attr_reader :secret_access_key
+
+      def client
+        @client ||= Aws::S3::Client.new(
+          {
+            region: region,
+            credentials: create_credentials
+          }.compact
+        )
+      end
+
+      def create_credentials
+        return nil if access_key.nil? || secret_access_key.nil?
 
-    def client
-      @client ||= Aws::S3::Client.new
+        Aws::Credentials.new(
+          access_key,
+          secret_access_key
+        )
+      end
     end
   end
 end

fastlane/spec/helper/s3_client_helper_spec.rb

@@ -1,5 +1,5 @@
 describe Fastlane::Helper::S3ClientHelper do
-  subject { described_class.new }
+  subject { described_class.new(s3_client: instance_double('Aws::S3::Client')) }
 
   describe '#find_bucket!' do
     before { class_double('Aws::S3::Bucket', new: bucket).as_stubbed_const }