Add AWS web identity token file to list of available services to fetch credentials

Add test coverage for web identity token file

Gemfile

@@ -6,6 +6,7 @@ gemspec
 group :test, :default do
   gem 'pry-nav'
   gem 'mime-types', '~> 3.1'
+  gem 'nokogiri', '~> 1.10.10'
 end
 
 group :test do

lib/fog/aws/credential_fetcher.rb

@@ -1,3 +1,7 @@
+# frozen_string_literal: true
+
+require "nokogiri"
+
 module Fog
   module AWS
     module CredentialFetcher
@@ -9,6 +13,8 @@ module Fog
 
       CONTAINER_CREDENTIALS_HOST = "http://169.254.170.2"
 
+      STS_GLOBAL_ENDPOINT = "https://sts.amazonaws.com"
+
       module ServiceMethods
         def fetch_credentials(options)
           if options[:use_iam_profile] && Fog.mocking?
@@ -23,6 +29,30 @@ module Fog
                 connection = options[:connection] || Excon.new(CONTAINER_CREDENTIALS_HOST)
                 credential_path = options[:credential_path] || ENV["AWS_CONTAINER_CREDENTIALS_RELATIVE_URI"]
                 role_data = connection.get(:path => credential_path, :idempotent => true, :expects => 200).body
+                session = Fog::JSON.decode(role_data)
+
+                if region.nil?
+                  connection = options[:metadata_connection] || Excon.new(INSTANCE_METADATA_HOST)
+                  token_header = fetch_credentials_token_header(connection, options[:disable_imds_v2])
+                  region = connection.get(:path => INSTANCE_METADATA_AZ, :idempotent => true, :expects => 200, :headers => token_header).body[0..-2]
+                end
+              elsif ENV["AWS_WEB_IDENTITY_TOKEN_FILE"]
+                params = {
+                  :Action => "AssumeRoleWithWebIdentity",
+                  :RoleArn => options[:role_arn] || ENV.fetch("AWS_ROLE_ARN"),
+                  :RoleSessionName => options[:role_session_name] || ENV.fetch("AWS_ROLE_SESSION_NAME"),
+                  :WebIdentityToken => File.read(options[:aws_web_identity_token_file] || ENV.fetch("AWS_WEB_IDENTITY_TOKEN_FILE")),
+                  :Version => "2011-06-15",
+                }
+                connection = options[:connection] || Excon.new(STS_GLOBAL_ENDPOINT, :query => params)
+                document = Nokogiri::XML(connection.get(:idempotent => true, :expects => 200).body)
+
+                session = {
+                  "AccessKeyId" => document.css("AccessKeyId").children.text,
+                  "SecretAccessKey" => document.css("SecretAccessKey").children.text,
+                  "Token" => document.css("SessionToken").children.text,
+                  "Expiration" => document.css("Expiration").children.text,
+                }
 
                 if region.nil?
                   connection = options[:metadata_connection] || Excon.new(INSTANCE_METADATA_HOST)
@@ -34,10 +64,11 @@ module Fog
                 token_header = fetch_credentials_token_header(connection, options[:disable_imds_v2])
                 role_name = connection.get(:path => INSTANCE_METADATA_PATH, :idempotent => true, :expects => 200, :headers => token_header).body
                 role_data = connection.get(:path => INSTANCE_METADATA_PATH+role_name, :idempotent => true, :expects => 200, :headers => token_header).body
+                session = Fog::JSON.decode(role_data)
+                
                 region ||= connection.get(:path => INSTANCE_METADATA_AZ, :idempotent => true, :expects => 200, :headers => token_header).body[0..-2]
               end
               
-              session = Fog::JSON.decode(role_data)
               credentials = {}
               credentials[:aws_access_key_id] = session['AccessKeyId']
               credentials[:aws_secret_access_key] = session['SecretAccessKey']

tests/credentials_tests.rb

@@ -60,6 +60,35 @@ Shindo.tests('AWS | credentials', ['aws']) do
 
     ENV['AWS_CONTAINER_CREDENTIALS_RELATIVE_URI'] = nil
 
+    ENV['AWS_WEB_IDENTITY_TOKEN_FILE'] = File.dirname(__FILE__) + '/lorem.txt'
+    ENV['AWS_ROLE_ARN'] = "dummyrole"
+    ENV['AWS_ROLE_SESSION_NAME'] = "dummyrolesessionname"
+    document = 
+      '<AssumeRoleWithWebIdentityResponse xmlns="https://sts.amazonaws.com/doc/2011-06-15/">'\
+        '<AssumeRoleWithWebIdentityResult>'\
+          '<Credentials>'\
+            '<SessionToken>dummytoken</SessionToken>'\
+            '<SecretAccessKey>dummysecret</SecretAccessKey>'\
+            "<Expiration>#{expires_at.xmlschema}</Expiration>"\
+            '<AccessKeyId>dummykey</AccessKeyId>'\
+          '</Credentials>'\
+        '</AssumeRoleWithWebIdentityResult>'\
+      '</AssumeRoleWithWebIdentityResponse>'
+    
+    Excon.stub({method: :get, path: "/", idempotent: true}, { status: 200, body: document})
+
+    tests('#fetch_credentials token based') do
+      returns(
+        aws_access_key_id: 'dummykey',
+        aws_secret_access_key: 'dummysecret',
+        aws_session_token: 'dummytoken',
+        region: 'us-west-1',
+        aws_credentials_expire_at: expires_at
+      ) { Fog::AWS::Compute.fetch_credentials(use_iam_profile: true) }
+    end
+
+    ENV['AWS_WEB_IDENTITY_TOKEN_FILE'] = nil
+
     compute = Fog::AWS::Compute.new(use_iam_profile: true)
 
     tests('#refresh_credentials_if_expired') do
@@ -100,6 +129,7 @@ Shindo.tests('AWS | credentials', ['aws']) do
     end
   ensure
     ENV['AWS_CONTAINER_CREDENTIALS_RELATIVE_URI'] = nil
+    ENV['AWS_WEB_IDENTITY_TOKEN_FILE'] = nil
     Excon.stubs.clear
     Excon.defaults[:mock] = old_mock_value
     Fog.mock! if fog_was_mocked