solved the problem, with base64 library.

Gemfile

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #-------------------------------------------------------------------------
 # # Copyright (c) Microsoft and contributors. All rights reserved.
 #
@@ -13,4 +15,4 @@
 # limitations under the License.
 #--------------------------------------------------------------------------
 source 'https://rubygems.org'
-gemspec
+gemspec

Rakefile

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #-------------------------------------------------------------------------
 # # Copyright (c) Microsoft and contributors. All rights reserved.
 #
@@ -22,27 +24,25 @@ Gem::PackageTask.new(gem_spec) do |pkg|
 end
 
 namespace :test do
-
   Rake::TestTask.new :unit do |t|
     t.pattern = 'test/unit/**/*_test.rb'
     t.verbose = true
-    t.libs = %w(lib test)
+    t.libs = %w[lib test]
   end
 
   namespace :unit do
     def component_task(component)
       Rake::TestTask.new component do |t|
         t.pattern = "test/unit/#{component}/**/*_test.rb"
         t.verbose = true
-        t.libs = %w(lib test)
+        t.libs = %w[lib test]
       end
     end
 
     component_task :core
   end
-
 end
 
-task :test => %w(test:unit)
+task test: %w[test:unit]
 
-task :default => :test
+task default: :test

azure-core.gemspec

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #-------------------------------------------------------------------------
 # # Copyright (c) Microsoft and contributors. All rights reserved.
 #
@@ -14,7 +16,7 @@
 #--------------------------------------------------------------------------
 require 'date'
 
-require File.expand_path('../lib/azure/core/version', __FILE__)
+require File.expand_path('lib/azure/core/version', __dir__)
 
 Gem::Specification.new do |s|
   s.name    = 'azure-core'
@@ -25,20 +27,19 @@ Gem::Specification.new do |s|
   s.summary     = 'Core library to be consumed by Ruby SDK gems'
   s.homepage    = 'http://github.com/Azure/azure-ruby-asm-core'
   s.license     = 'Apache License, Version 2.0'
-  s.files       = `git ls-files`.split("\n").reject { |f|  f.start_with?("test/unit") }
+  s.files       = `git ls-files`.split("\n").reject { |f| f.start_with?('test/unit') }
 
   s.required_ruby_version = '>= 1.9.3'
 
   s.add_runtime_dependency('faraday',                 '~> 0.9')
   s.add_runtime_dependency('faraday_middleware',      '~> 0.10')
   s.add_runtime_dependency('nokogiri',                '~> 1.6')
 
+  s.add_development_dependency('bundler',             '~> 1.11')
   s.add_development_dependency('dotenv',              '~> 2.0')
   s.add_development_dependency('minitest',            '~> 5')
   s.add_development_dependency('minitest-reporters',  '~> 1')
   s.add_development_dependency('mocha',               '~> 1.0')
   s.add_development_dependency('rake',                '~> 10.0')
   s.add_development_dependency('timecop',             '~> 0.7')
-  s.add_development_dependency('bundler',             '~> 1.11')
-
 end

lib/azure/core/auth/signer.rb

@@ -31,8 +31,7 @@ def initialize(access_key)
           if access_key.nil?
             raise ArgumentError, 'Signing key must be provided'
           end
-
-          @access_key = Base64.strict_decode64(access_key)
+          @access_key = Base64.decode64(access_key)
         end
 
         # Generate an HMAC signature.