diff --git a/.github/dependabot.yml b/.github/dependabot.yml
new file mode 100644
index 00000000..a0267668
--- /dev/null
+++ b/.github/dependabot.yml
@@ -0,0 +1,8 @@
+version: 2
+updates:
+  - package-ecosystem: bundler
+    directory: "/"
+    schedule:
+      interval: daily
+      time: "04:28"
+    open-pull-requests-limit: 10
\ No newline at end of file
diff --git a/.github/workflows/style.yml b/.github/workflows/style.yml
new file mode 100644
index 00000000..fd211ace
--- /dev/null
+++ b/.github/workflows/style.yml
@@ -0,0 +1,37 @@
+name: Code Style Checks
+
+on:
+  push:
+    branches:
+      - 'main'
+      - 'master'
+      - '*-maintenance'
+      - '*-dev'
+    tags:
+      - '!*' # Do not execute on tags
+  pull_request:
+    branches:
+      - '*'
+
+jobs:
+  rubocop:
+    name: Rubocop
+    if: "!contains(github.event.commits[0].message, '[ci skip]') && !contains(github.event.commits[0].message, '[skip ci]')"
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby:
+          - 2.7
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true
+      - name: Install dependencies
+        run: bundle install --jobs 3 --retry 3
+      - name: Run Rubocop
+        run: bundle exec rubocop -DESP
\ No newline at end of file
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 00000000..9d0352ab
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,58 @@
+name: Unit Tests
+
+on:
+  push:
+    branches:
+      - 'main'
+      - 'master'
+      - '*-maintenance'
+      - '*-dev'
+    tags:
+      - '!*' # Do not execute on tags
+  pull_request:
+    branches:
+      - '*'
+
+jobs:
+  test:
+    name: Specs - Ruby ${{ matrix.ruby }} ${{ matrix.name_extra || '' }}
+    if: "!contains(github.event.commits[0].message, '[ci skip]') && !contains(github.event.commits[0].message, '[skip ci]')"
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby:
+          - 3.0.0
+          - 2.7
+          - 2.6
+          - 2.5
+          - 2.4
+          - 2.3
+          - 2.2
+          - 2.1
+    runs-on: ubuntu-20.04
+    continue-on-error: ${{ matrix.allow_failure || endsWith(matrix.ruby, 'head') }}
+    steps:
+      - uses: amancevice/setup-code-climate@v0
+        name: CodeClimate Install
+        if: matrix.ruby == '2.7' && github.event_name != 'pull_request'
+        with:
+          cc_test_reporter_id: ${{ secrets.CC_TEST_REPORTER_ID }}
+      - uses: actions/checkout@v2
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          bundler: ${{ matrix.bundler || 2 }}
+          bundler-cache: true
+          ruby-version: ${{ matrix.ruby }}
+      - name: Install dependencies
+        run: bundle install --jobs 3 --retry 3 --binstubs --standalone
+      - name: CodeClimate Pre-build Notification
+        run: cc-test-reporter before-build
+        if: matrix.ruby == '2.7' && github.event_name != 'pull_request'
+        continue-on-error: ${{ matrix.allow_failures != 'false' }}
+      - name: Run tests
+        run: bundle exec rake test
+      - name: CodeClimate Post-build Notification
+        run: cc-test-reporter after-build
+        if: matrix.ruby == '2.7' && github.event_name != 'pull_request' && always()
+        continue-on-error: ${{ matrix.allow_failures != 'false' }}
diff --git a/.gitignore b/.gitignore
index 36762cf9..6480a03a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -16,4 +16,4 @@ rdoc/*
 /gemfiles/*.gemfile.lock
 
 # CI bundle
-/gemfiles/vendor/
\ No newline at end of file
+/gemfiles/vendor/
diff --git a/.rspec b/.rspec
index 09127182..3629a4a1 100644
--- a/.rspec
+++ b/.rspec
@@ -1,2 +1,4 @@
 --color
 --order random
+--require helper
+--format=documentation
diff --git a/.rubocop.yml b/.rubocop.yml
index c6a41973..3c1afd65 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -1,30 +1,42 @@
-require: rubocop-rspec
 inherit_from:
   - .rubocop_todo.yml
   - .rubocop_rspec.yml
+
+require:
+  - 'rubocop-md'
+  - 'rubocop-packaging'
+  - 'rubocop-performance'
+  - 'rubocop-rake'
+  - 'rubocop-rspec'
+
 AllCops:
+  NewCops: enable
   DisplayCopNames: true # Display the name of the failing cops
-  TargetRubyVersion: 2.1
   Exclude:
     - 'gemfiles/vendor/**/*'
     - 'vendor/**/*'
     - '**/.irbrc'
 
-Gemspec/RequiredRubyVersion:
-  Enabled: false
-
 Metrics/BlockLength:
+  IgnoredMethods:
+    - context
+    - describe
+    - it
+    - shared_context
+    - shared_examples
+    - shared_examples_for
+    - namespace
+    - draw
+
+Gemspec/RequiredRubyVersion:
   Enabled: false
 
 Metrics/BlockNesting:
   Max: 2
 
-Metrics/LineLength:
+Layout/LineLength:
   Enabled: false
 
-Metrics/MethodLength:
-  Max: 15
-
 Metrics/ParameterLists:
   Max: 4
 
@@ -78,3 +90,23 @@ Style/TrailingCommaInArrayLiteral:
 
 Style/TrailingCommaInHashLiteral:
   EnforcedStyleForMultiline: comma
+
+Style/HashSyntax:
+  EnforcedStyle: hash_rockets
+
+Style/Lambda:
+  Enabled: false
+
+Style/SymbolArray:
+  Enabled: false
+
+Style/EachWithObject:
+  Enabled: false
+
+# Once we drop Rubies that lack support for __dir__ we can turn this on.
+Style/ExpandPathArguments:
+  Enabled: false
+
+# On Ruby 1.9 array.to_h isn't available, needs to be Hash[array]
+Style/HashConversion:
+  Enabled: false
\ No newline at end of file
diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
index e7701734..f430c2d1 100644
--- a/.rubocop_todo.yml
+++ b/.rubocop_todo.yml
@@ -1,15 +1,113 @@
-Style/HashSyntax:
-  EnforcedStyle: hash_rockets
+# This configuration was generated by
+# `rubocop --auto-gen-config`
+# on 2021-03-18 18:59:52 UTC using RuboCop version 1.11.0.
+# The point is for the user to remove these configuration records
+# one by one as the offenses are removed from the code base.
+# Note that changes in the inspected code, or installation of new
+# versions of RuboCop, may require this file to be generated again.
 
-Style/Lambda:
-  Enabled: false
+# Offense count: 1
+# Configuration parameters: AllowedMethods.
+# AllowedMethods: enums
+Lint/ConstantDefinitionInBlock:
+  Exclude:
+    - 'spec/oauth2/client_spec.rb'
 
-Style/SymbolArray:
-  Enabled: false
+# Offense count: 1
+Lint/UselessAssignment:
+  Exclude:
+    - '**/*.md'
+    - '**/*.markdown'
+    - 'spec/oauth2/client_spec.rb'
 
-Style/EachWithObject:
-  Enabled: false
+# Offense count: 1
+# Configuration parameters: CountComments, CountAsOne, ExcludedMethods, IgnoredMethods.
+# IgnoredMethods: refine
+Metrics/BlockLength:
+  Max: 27
+
+# Offense count: 4
+# Configuration parameters: IgnoredMethods.
+Metrics/CyclomaticComplexity:
+  Max: 11
+
+# Offense count: 1
+# Configuration parameters: CountComments, CountAsOne, ExcludedMethods, IgnoredMethods.
+Metrics/MethodLength:
+  Max: 18
+
+# Offense count: 3
+# Configuration parameters: IgnoredMethods.
+Metrics/PerceivedComplexity:
+  Max: 11
+
+# Offense count: 14
+# Configuration parameters: EnforcedStyle, CheckMethodNames, CheckSymbols, AllowedIdentifiers.
+# SupportedStyles: snake_case, normalcase, non_integer
+# AllowedIdentifiers: capture3, iso8601, rfc1123_date, rfc822, rfc2822, rfc3339
+Naming/VariableNumber:
+  Exclude:
+    - 'Gemfile'
+
+# Offense count: 1
+Packaging/GemspecGit:
+  Exclude:
+    - 'oauth2.gemspec'
 
-# Once we drop Rubies that lack support for __dir__ we can turn this on.
-Style/ExpandPathArguments:
+# Offense count: 2
+# Configuration parameters: MinSize.
+Performance/CollectionLiteralInLoop:
+  Exclude:
+    - 'spec/oauth2/strategy/auth_code_spec.rb'
+    - 'spec/oauth2/strategy/client_credentials_spec.rb'
+
+# Offense count: 7
+# Configuration parameters: Prefixes.
+# Prefixes: when, with, without
+RSpec/ContextWording:
+  Exclude:
+    - 'spec/oauth2/access_token_spec.rb'
+    - 'spec/oauth2/authenticator_spec.rb'
+    - 'spec/oauth2/client_spec.rb'
+
+# Offense count: 1
+RSpec/LeakyConstantDeclaration:
+  Exclude:
+    - 'spec/oauth2/client_spec.rb'
+
+# Offense count: 8
+# Configuration parameters: AllowSubject.
+RSpec/MultipleMemoizedHelpers:
+  Max: 6
+
+# Offense count: 1
+Rake/Desc:
+  Exclude:
+    - 'Rakefile'
+
+# Offense count: 40
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: always, always_true, never
+Style/FrozenStringLiteralComment:
   Enabled: false
+
+# Offense count: 1
+Style/MixinUsage:
+  Exclude:
+    - 'spec/helper.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: ConvertCodeThatCanStartToReturnNil, AllowedMethods.
+# AllowedMethods: present?, blank?, presence, try, try!
+Style/SafeNavigation:
+  Exclude:
+    - 'lib/oauth2/error.rb'
+
+# Offense count: 3
+# Cop supports --auto-correct.
+Style/StringConcatenation:
+  Exclude:
+    - 'lib/oauth2/authenticator.rb'
+    - 'spec/oauth2/authenticator_spec.rb'
diff --git a/.ruby-version b/.ruby-version
index 68b3a4cd..24ba9a38 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-1.9.3-p551
+2.7.0
diff --git a/.travis.yml b/.travis.yml
index 79b25172..26059437 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -19,10 +19,23 @@ before_install:
       gem install --no-document bundler "bundler:>=2.0"
     fi
 
+before_script:
+  - curl -L https://codeclimate.com/downloads/test-reporter/test-reporter-latest-linux-amd64 > ./cc-test-reporter
+  - chmod +x ./cc-test-reporter
+  - ./cc-test-reporter before-build
+
+after_script:
+  - ./cc-test-reporter after-build --exit-code $TRAVIS_TEST_RESULT
+
 bundler_args: --no-deployment --jobs 3 --retry 3
 
 cache: bundler
 
+env:
+  global:
+    - JRUBY_OPTS="$JRUBY_OPTS -Xcli.debug=true --debug"
+    - CC_TEST_REPORTER_ID=29caf9cf27d27ae609c088feb9d4ba34460f7a39251f2e8615c9a16f3075530e
+
 language: ruby
 
 matrix:
@@ -30,8 +43,9 @@ matrix:
     - rvm: jruby-head
     - rvm: ruby-head
     - rvm: truffleruby
-    - rvm: jruby-9.0 # targets MRI v2.0
-      gemfile: gemfiles/jruby_9.0.gemfile
+    - rvm: jruby-9.0
+    - rvm: jruby-9.1 # jruby-9.1 often fails to download, thus failing the build.
+    - rvm: jruby-9.2 # jruby-9.2 often fails to download, thus failing the build.
   fast_finish: true
   include:
 #    - rvm: jruby-1.7 # targets MRI v1.9
@@ -40,29 +54,22 @@ matrix:
       gemfile: gemfiles/ruby_1.9.gemfile
     - rvm: 2.0
       gemfile: gemfiles/ruby_2.0.gemfile
-    - rvm: 2.1
-      gemfile: gemfiles/ruby_2.1.gemfile
+    - rvm: jruby-9.0 # targets MRI v2.0
+      gemfile: gemfiles/jruby_9.0.gemfile
     # DEPRECATION WARNING
+    # NOTE: Specs for Ruby 2.1 are now running with Github Actions
     # oauth2 1.x series releases are the last to support Ruby versions above
     # oauth2 2.x series releases will support Ruby versions below, and not above
+    # NOTE: Specs for Ruby 2.2, 2.3, 2.4, 2.5, 2.6, 2.7 & 3.0 are now running with Github Actions
     - rvm: jruby-9.1 # targets MRI v2.3
       gemfile: gemfiles/jruby_9.1.gemfile
-    - rvm: 2.2
-      gemfile: gemfiles/ruby_2.2.gemfile
-    - rvm: 2.3
-      gemfile: gemfiles/ruby_2.3.gemfile
-    - rvm: 2.4
-      gemfile: gemfiles/ruby_2.4.gemfile
     - rvm: jruby-9.2 # targets MRI v2.5
       gemfile: gemfiles/jruby_9.2.gemfile
-    - rvm: 2.5
-      gemfile: gemfiles/ruby_2.5.gemfile
-    - rvm: 2.6
-      gemfile: gemfiles/ruby_2.6.gemfile
     - rvm: jruby-head
       gemfile: gemfiles/jruby_head.gemfile
     - rvm: ruby-head
       gemfile: gemfiles/ruby_head.gemfile
     - rvm: truffleruby
+      gemfile: gemfiles/truffleruby.gemfile
 
 sudo: false
diff --git a/CHANGELOG.md b/CHANGELOG.md
index fa957410..2d6ad964 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,9 +1,34 @@
 # Change Log
 All notable changes to this project will be documented in this file.
 
-## [unreleased]
+## unreleased
 
-- no changes yet
+## [1.4.6] - 2021-03-18
+
+- [#537](https://github.com/oauth-xx/oauth2/pull/537) - Fix crash in OAuth2::Client#get_token (@anderscarling)
+- [#538](https://github.com/oauth-xx/oauth2/pull/538) - Remove reliance on globally included OAuth2 in tests for version 1.4 (@anderscarling)
+- [#540](https://github.com/oauth-xx/oauth2/pull/540) - Add Oauth::Version::VERSION constant (@pboling)
+
+## [1.4.5] - 2021-03-18
+
+- [#535](https://github.com/oauth-xx/oauth2/pull/535) - Compatibility with range of supported Ruby OpenSSL versions, Rubocop updates, Github Actions (@pboling)
+- [#518](https://github.com/oauth-xx/oauth2/pull/518) - Add extract_access_token option to OAuth2::Client (@jonspalmer)
+
+## [1.4.4] - 2020-02-12
+
+- [#408](https://github.com/oauth-xx/oauth2/pull/408) - Fixed expires_at for formatted time (@Lomey)
+
+## [1.4.3] - 2020-01-29
+
+- [#483](https://github.com/oauth-xx/oauth2/pull/483) - add project metadata to gemspec (@orien)
+- [#495](https://github.com/oauth-xx/oauth2/pull/495) - support additional types of access token requests (@SteveyblamFreeagent, @thomcorley, @dgholz)
+  - Adds support for private_key_jwt and tls_client_auth
+- [#433](https://github.com/oauth-xx/oauth2/pull/433) - allow field names with square brackets and numbers in params (@asm256)
+
+## [1.4.2] - 2019-10-01
+
+- [#478](https://github.com/oauth-xx/oauth2/pull/478) - support latest version of faraday & fix build (@pboling)
+  - officially support Ruby 2.6 and truffleruby
 
 ## [1.4.1] - 2018-10-13
 
@@ -136,4 +161,6 @@ All notable changes to this project will be documented in this file.
 [1.3.1]: https://github.com/oauth-xx/oauth2/compare/v1.3.0...v1.3.1
 [1.4.0]: https://github.com/oauth-xx/oauth2/compare/v1.3.1...v1.4.0
 [1.4.1]: https://github.com/oauth-xx/oauth2/compare/v1.4.0...v1.4.1
+[1.4.2]: https://github.com/oauth-xx/oauth2/compare/v1.4.1...v1.4.2
+[1.4.3]: https://github.com/oauth-xx/oauth2/compare/v1.4.2...v1.4.3
 [unreleased]: https://github.com/oauth-xx/oauth2/compare/v1.4.1...HEAD
diff --git a/CODE_OF_CONDUCT.md b/CODE_OF_CONDUCT.md
index 395b407d..99ab478b 100644
--- a/CODE_OF_CONDUCT.md
+++ b/CODE_OF_CONDUCT.md
@@ -1,74 +1,133 @@
+
 # Contributor Covenant Code of Conduct
 
 ## Our Pledge
 
-In the interest of fostering an open and welcoming environment, we as
-contributors and maintainers pledge to making participation in our project and
-our community a harassment-free experience for everyone, regardless of age, body
-size, disability, ethnicity, gender identity and expression, level of experience,
-nationality, personal appearance, race, religion, or sexual identity and
-orientation.
+We as members, contributors, and leaders pledge to make participation in our
+community a harassment-free experience for everyone, regardless of age, body
+size, visible or invisible disability, ethnicity, sex characteristics, gender
+identity and expression, level of experience, education, socio-economic status,
+nationality, personal appearance, race, religion, or sexual identity
+and orientation.
+
+We pledge to act and interact in ways that contribute to an open, welcoming,
+diverse, inclusive, and healthy community.
 
 ## Our Standards
 
-Examples of behavior that contributes to creating a positive environment
-include:
+Examples of behavior that contributes to a positive environment for our
+community include:
 
-* Using welcoming and inclusive language
-* Being respectful of differing viewpoints and experiences
-* Gracefully accepting constructive criticism
-* Focusing on what is best for the community
-* Showing empathy towards other community members
+* Demonstrating empathy and kindness toward other people
+* Being respectful of differing opinions, viewpoints, and experiences
+* Giving and gracefully accepting constructive feedback
+* Accepting responsibility and apologizing to those affected by our mistakes,
+  and learning from the experience
+* Focusing on what is best not just for us as individuals, but for the
+  overall community
 
-Examples of unacceptable behavior by participants include:
+Examples of unacceptable behavior include:
 
-* The use of sexualized language or imagery and unwelcome sexual attention or
-advances
-* Trolling, insulting/derogatory comments, and personal or political attacks
+* The use of sexualized language or imagery, and sexual attention or
+  advances of any kind
+* Trolling, insulting or derogatory comments, and personal or political attacks
 * Public or private harassment
-* Publishing others' private information, such as a physical or electronic
-  address, without explicit permission
+* Publishing others' private information, such as a physical or email
+  address, without their explicit permission
 * Other conduct which could reasonably be considered inappropriate in a
   professional setting
 
-## Our Responsibilities
+## Enforcement Responsibilities
 
-Project maintainers are responsible for clarifying the standards of acceptable
-behavior and are expected to take appropriate and fair corrective action in
-response to any instances of unacceptable behavior.
+Community leaders are responsible for clarifying and enforcing our standards of
+acceptable behavior and will take appropriate and fair corrective action in
+response to any behavior that they deem inappropriate, threatening, offensive,
+or harmful.
 
-Project maintainers have the right and responsibility to remove, edit, or
-reject comments, commits, code, wiki edits, issues, and other contributions
-that are not aligned to this Code of Conduct, or to ban temporarily or
-permanently any contributor for other behaviors that they deem inappropriate,
-threatening, offensive, or harmful.
+Community leaders have the right and responsibility to remove, edit, or reject
+comments, commits, code, wiki edits, issues, and other contributions that are
+not aligned to this Code of Conduct, and will communicate reasons for moderation
+decisions when appropriate.
 
 ## Scope
 
-This Code of Conduct applies both within project spaces and in public spaces
-when an individual is representing the project or its community. Examples of
-representing a project or community include using an official project e-mail
-address, posting via an official social media account, or acting as an appointed
-representative at an online or offline event. Representation of a project may be
-further defined and clarified by project maintainers.
+This Code of Conduct applies within all community spaces, and also applies when
+an individual is officially representing the community in public spaces.
+Examples of representing our community include using an official e-mail address,
+posting via an official social media account, or acting as an appointed
+representative at an online or offline event.
 
 ## Enforcement
 
 Instances of abusive, harassing, or otherwise unacceptable behavior may be
-reported by contacting the project team at peter.boling@gmail.com. All
-complaints will be reviewed and investigated and will result in a response that
-is deemed necessary and appropriate to the circumstances. The project team is
-obligated to maintain confidentiality with regard to the reporter of an incident.
-Further details of specific enforcement policies may be posted separately.
+reported to the community leaders responsible for enforcement at
+[INSERT CONTACT METHOD].
+All complaints will be reviewed and investigated promptly and fairly.
+
+All community leaders are obligated to respect the privacy and security of the
+reporter of any incident.
+
+## Enforcement Guidelines
+
+Community leaders will follow these Community Impact Guidelines in determining
+the consequences for any action they deem in violation of this Code of Conduct:
+
+### 1. Correction
+
+**Community Impact**: Use of inappropriate language or other behavior deemed
+unprofessional or unwelcome in the community.
+
+**Consequence**: A private, written warning from community leaders, providing
+clarity around the nature of the violation and an explanation of why the
+behavior was inappropriate. A public apology may be requested.
+
+### 2. Warning
 
-Project maintainers who do not follow or enforce the Code of Conduct in good
-faith may face temporary or permanent repercussions as determined by other
-members of the project's leadership.
+**Community Impact**: A violation through a single incident or series
+of actions.
+
+**Consequence**: A warning with consequences for continued behavior. No
+interaction with the people involved, including unsolicited interaction with
+those enforcing the Code of Conduct, for a specified period of time. This
+includes avoiding interactions in community spaces as well as external channels
+like social media. Violating these terms may lead to a temporary or
+permanent ban.
+
+### 3. Temporary Ban
+
+**Community Impact**: A serious violation of community standards, including
+sustained inappropriate behavior.
+
+**Consequence**: A temporary ban from any sort of interaction or public
+communication with the community for a specified period of time. No public or
+private interaction with the people involved, including unsolicited interaction
+with those enforcing the Code of Conduct, is allowed during this period.
+Violating these terms may lead to a permanent ban.
+
+### 4. Permanent Ban
+
+**Community Impact**: Demonstrating a pattern of violation of community
+standards, including sustained inappropriate behavior,  harassment of an
+individual, or aggression toward or disparagement of classes of individuals.
+
+**Consequence**: A permanent ban from any sort of public interaction within
+the community.
 
 ## Attribution
 
-This Code of Conduct is adapted from the [Contributor Covenant][homepage], version 1.4,
-available at [http://contributor-covenant.org/version/1/4][version]
+This Code of Conduct is adapted from the [Contributor Covenant][homepage],
+version 2.0, available at
+[https://www.contributor-covenant.org/version/2/0/code_of_conduct.html][v2.0].
+
+Community Impact Guidelines were inspired by
+[Mozilla's code of conduct enforcement ladder][Mozilla CoC].
+
+For answers to common questions about this code of conduct, see the FAQ at
+[https://www.contributor-covenant.org/faq][FAQ]. Translations are available
+at [https://www.contributor-covenant.org/translations][translations].
 
-[homepage]: http://contributor-covenant.org
-[version]: http://contributor-covenant.org/version/1/4/
+[homepage]: https://www.contributor-covenant.org
+[v2.0]: https://www.contributor-covenant.org/version/2/0/code_of_conduct.html
+[Mozilla CoC]: https://github.com/mozilla/diversity
+[FAQ]: https://www.contributor-covenant.org/faq
+[translations]: https://www.contributor-covenant.org/translations
diff --git a/Gemfile b/Gemfile
index 0dbce159..4657b438 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,29 +1,52 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
 
+gemspec
+
 git_source(:github) { |repo_name| "https://github.com/#{repo_name}" }
 
 gem 'faraday', ['>= 0.8', '< 2.0'], :platforms => [:jruby_18, :ruby_18]
 gem 'jwt', '< 1.5.2', :platforms => [:jruby_18, :ruby_18]
 gem 'rake', '< 11.0'
-gem 'rdoc', '~> 4.2.2'
 
-group :test do
-  ruby_version = Gem::Version.new(RUBY_VERSION)
-  if ruby_version >= Gem::Version.new('2.1')
-    # TODO: Upgrade to >= 0.59 when we drop Rubies below 2.2
-    #     Error: Unsupported Ruby version 2.1 found in `TargetRubyVersion` parameter (in .rubocop.yml). 2.1-compatible analysis was dropped after version 0.58.
-    #     Supported versions: 2.2, 2.3, 2.4, 2.5
-    gem 'rubocop', '~> 0.57.0'
-    gem 'rubocop-rspec', '~> 1.27.0' # last version that can use rubocop < 0.58
+ruby_version = Gem::Version.new(RUBY_VERSION)
+
+### deps for documentation and rdoc.info
+group :documentation do
+  gem 'github-markup', :platform => :mri
+  gem 'rdoc'
+  gem 'redcarpet', :platform => :mri
+  gem 'yard', :require => false
+end
+
+group :development, :test do
+  if ruby_version >= Gem::Version.new('2.4')
+    # No need to run byebug / pry on earlier versions
+    gem 'byebug', :platform => :mri
+    gem 'pry', :platform => :mri
+    gem 'pry-byebug', :platform => :mri
   end
-  gem 'pry', '~> 0.11' if ruby_version >= Gem::Version.new('2.0')
 
+  if ruby_version >= Gem::Version.new('2.7')
+    # No need to run rubocop or simplecov on earlier versions
+    gem 'rubocop', '~> 1.9', :platform => :mri
+    gem 'rubocop-md', :platform => :mri
+    gem 'rubocop-packaging', :platform => :mri
+    gem 'rubocop-performance', :platform => :mri
+    gem 'rubocop-rake', :platform => :mri
+    gem 'rubocop-rspec', :platform => :mri
+
+    gem 'coveralls'
+    gem 'simplecov', :platform => :mri
+  end
+end
+
+group :test do
   gem 'addressable', '~> 2.3.8'
   gem 'backports'
-  gem 'coveralls'
   gem 'rack', '~> 1.2', :platforms => [:jruby_18, :jruby_19, :ruby_18, :ruby_19, :ruby_20, :ruby_21]
   gem 'rspec', '>= 3'
-  gem 'simplecov', '>= 0.9'
 
   platforms :jruby_18, :ruby_18 do
     gem 'mime-types', '~> 1.25'
@@ -36,5 +59,3 @@ group :test do
     gem 'tins', '< 1.7'
   end
 end
-
-gemspec
diff --git a/README.md b/README.md
index 77054ded..8cff087e 100644
--- a/README.md
+++ b/README.md
@@ -1,10 +1,26 @@
 # OAuth2
 
+If you need the readme for a released version of the gem please find it below:
+
+| Version  | Release Date | Readme                                                   |
+|----------|--------------|----------------------------------------------------------|
+| 1.4.4    | Feb 12, 2020 | https://github.com/oauth-xx/oauth2/blob/v1.4.4/README.md |
+| 1.4.3    | Jan 29, 2020 | https://github.com/oauth-xx/oauth2/blob/v1.4.3/README.md |
+| 1.4.2    | Oct 1, 2019  | https://github.com/oauth-xx/oauth2/blob/v1.4.2/README.md |
+| 1.4.1    | Oct 13, 2018 | https://github.com/oauth-xx/oauth2/blob/v1.4.1/README.md |
+| 1.4.0    | Jun 9, 2017  | https://github.com/oauth-xx/oauth2/blob/v1.4.0/README.md |
+| 1.3.1    | Mar 3, 2017  | https://github.com/oauth-xx/oauth2/blob/v1.3.1/README.md |
+| 1.3.0    | Dec 27, 2016 | https://github.com/oauth-xx/oauth2/blob/v1.3.0/README.md |
+| 1.2.0    | Jun 30, 2016 | https://github.com/oauth-xx/oauth2/blob/v1.2.0/README.md |
+| 1.1.0    | Jan 30, 2016 | https://github.com/oauth-xx/oauth2/blob/v1.1.0/README.md |
+| 1.0.0    | May 23, 2014 | https://github.com/oauth-xx/oauth2/blob/v1.0.0/README.md |
+| < 1.0.0  | Find here    | https://github.com/oauth-xx/oauth2/tags                  |
+
 [![Gem Version](http://img.shields.io/gem/v/oauth2.svg)][gem]
 [![Total Downloads](https://img.shields.io/gem/dt/oauth2.svg)][gem]
 [![Downloads Today](https://img.shields.io/gem/rt/oauth2.svg)][gem]
 [![Build Status](https://travis-ci.org/oauth-xx/oauth2.svg?branch=1-4-stable)][travis]
-[![Coverage Status](http://img.shields.io/coveralls/intridea/oauth2.svg)][coveralls]
+[![Test Coverage](https://api.codeclimate.com/v1/badges/688c612528ff90a46955/test_coverage)][codeclimate-coverage]
 [![Maintainability](https://api.codeclimate.com/v1/badges/688c612528ff90a46955/maintainability)][codeclimate-maintainability]
 [![Depfu](https://badges.depfu.com/badges/6d34dc1ba682bbdf9ae2a97848241743/count.svg)][depfu]
 [![Open Source Helpers](https://www.codetriage.com/oauth-xx/oauth2/badges/users.svg)][code-triage]
@@ -16,10 +32,12 @@
 [travis]: http://travis-ci.org/oauth-xx/oauth2
 [coveralls]: https://coveralls.io/r/oauth-xx/oauth2
 [codeclimate-maintainability]: https://codeclimate.com/github/oauth-xx/oauth2/maintainability
+[codeclimate-coverage]: https://codeclimate.com/github/oauth-xx/oauth2/test_coverage
 [depfu]: https://depfu.com/github/oauth-xx/oauth2
 [source-license]: https://opensource.org/licenses/MIT
 [inch-ci]: http://inch-ci.org/github/oauth-xx/oauth2
 [code-triage]: https://www.codetriage.com/oauth-xx/oauth2
+[fossa1]: https://app.fossa.io/projects/git%2Bgithub.com%2Foauth-xx%2Foauth2?ref=badge_shield
 
 A Ruby wrapper for the [OAuth 2.0 specification][oauth2-spec].
 
@@ -49,7 +67,7 @@ Or install it yourself as:
 
 [code]: https://github.com/oauth-xx/oauth2
 [issues]: https://github.com/oauth-xx/oauth2/issues
-[wiki]: https://github.com/oauth-xx/oauth2/wiki
+[wiki]: https://wiki.github.com/oauth-xx/oauth2
 
 ## Usage Examples
 
@@ -61,11 +79,12 @@ client.auth_code.authorize_url(:redirect_uri => 'http://localhost:8080/oauth2/ca
 # => "https://example.org/oauth/authorization?response_type=code&client_id=client_id&redirect_uri=http://localhost:8080/oauth2/callback"
 
 token = client.auth_code.get_token('authorization_code_value', :redirect_uri => 'http://localhost:8080/oauth2/callback', :headers => {'Authorization' => 'Basic some_password'})
-response = token.get('/api/resource', :params => { 'query_foo' => 'bar' })
+response = token.get('/api/resource', :params => {'query_foo' => 'bar'})
 response.class.name
 # => OAuth2::Response
 ```
 ## OAuth2::Response
+
 The AccessToken methods #get, #post, #put and #delete and the generic #request
 will return an instance of the #OAuth2::Response class.
 
@@ -78,12 +97,14 @@ The original response body, headers, and status can be accessed via their
 respective methods.
 
 ## OAuth2::AccessToken
+
 If you have an existing Access Token for a user, you can initialize an instance
 using various class methods including the standard new, from_hash (if you have
 a hash of the values), or from_kvform (if you have an
 application/x-www-form-urlencoded encoded string of the values).
 
 ## OAuth2::Error
+
 On 400+ status code responses, an OAuth2::Error will be raised.  If it is a
 standard OAuth2 error response, the body will be parsed and #code and #description will contain the values provided from the error and
 error_description parameters.  The #response property of OAuth2::Error will
@@ -95,6 +116,7 @@ instance will be returned as usual and on 400+ status code responses, the
 Response instance will contain the OAuth2::Error instance.
 
 ## Authorization Grants
+
 Currently the Authorization Code, Implicit, Resource Owner Password Credentials, Client Credentials, and Assertion
 authentication grant types have helper strategy classes that simplify client
 use.  They are available via the #auth_code, #implicit, #password, #client_credentials, and #assertion methods respectively.
@@ -129,29 +151,34 @@ requests for tokens for any Authentication grant type.
 This library aims to support and is [tested against][travis] the following Ruby
 implementations:
 
-### Rubies with support ending at Oauth2 2.x
+### Rubies with support ending at Oauth2 1.x
 
 * Ruby 1.9.3
+  - [JRuby 1.7][jruby-1.7] (targets MRI v1.9)
+
 * Ruby 2.0.0
+  - [JRuby 9.0][jruby-9.0] (targets MRI v2.0)
 * Ruby 2.1
-* Ruby 2.2
-* [JRuby 1.7][jruby-1.7] (targets MRI v1.9)
-* [JRuby 9.0][jruby-9.0] (targets MRI v2.0)
 
 ---
 
 ### Rubies with continued support past Oauth2 2.x
 
-* Ruby 2.3 - Support through version 3.x series
-* Ruby 2.4
-* Ruby 2.5
-* [JRuby 9.1][jruby-9.1] (targets MRI v2.3) 
-* [JRuby 9.2][jruby-9.2] (targets MRI v2.5)
+* Ruby 2.2 - Support ends with version 2.x series
+* Ruby 2.3 - Support ends with version 3.x series
+  - [JRuby 9.1][jruby-9.1] (targets MRI v2.3)
+* Ruby 2.4 - Support ends with version 4.x series
+* Ruby 2.5 - Support ends with version 5.x series
+  - [JRuby 9.2][jruby-9.2] (targets MRI v2.5)
+  - [truffleruby][truffleruby] (targets MRI 2.5)
+* Ruby 2.6 - Support ends with version 6.x series
+* Ruby 2.7 - Support ends with version 7.x series
 
 [jruby-1.7]: https://www.jruby.org/2017/05/11/jruby-1-7-27.html
 [jruby-9.0]: https://www.jruby.org/2016/01/26/jruby-9-0-5-0.html
 [jruby-9.1]: https://www.jruby.org/2017/05/16/jruby-9-1-9-0.html
 [jruby-9.2]: https://www.jruby.org/2018/05/24/jruby-9-2-0-0.html
+[truffleruby]: https://github.com/oracle/truffleruby
 
 If something doesn't work on one of these interpreters, it's a bug.
 
@@ -203,7 +230,7 @@ spec.add_dependency 'oauth2', '~> 1.4'
 
 ## Development
 
-After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.
+After checking out the repo, run `bundle install` to install dependencies. Then, run `rake spec` to run the tests.
 
 To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).
 
diff --git a/Rakefile b/Rakefile
index 1066a1b6..19bdfa31 100644
--- a/Rakefile
+++ b/Rakefile
@@ -33,7 +33,7 @@ end
 
 namespace :doc do
   require 'rdoc/task'
-  require File.expand_path('../lib/oauth2/version', __FILE__)
+  require 'oauth2/version'
   RDoc::Task.new do |rdoc|
     rdoc.rdoc_dir = 'rdoc'
     rdoc.title = "oauth2 #{OAuth2::Version}"
diff --git a/gemfiles/jruby_1.7.gemfile b/gemfiles/jruby_1.7.gemfile
index bbef7523..276621ef 100644
--- a/gemfiles/jruby_1.7.gemfile
+++ b/gemfiles/jruby_1.7.gemfile
@@ -4,7 +4,7 @@ gem 'faraday', '~> 0.15.4'
 
 gem 'json', '< 2.0'
 gem 'rack', '~> 1.2'
-gem 'rake', [">= 10.0", "< 12"]
+gem 'rake', ['>= 10.0', '< 12']
 gem 'term-ansicolor', '< 1.4.0'
 gem 'tins', '< 1.7'
 
diff --git a/gemfiles/jruby_9.0.gemfile b/gemfiles/jruby_9.0.gemfile
index 13fd08d3..6d3ebd53 100644
--- a/gemfiles/jruby_9.0.gemfile
+++ b/gemfiles/jruby_9.0.gemfile
@@ -2,6 +2,6 @@ source 'https://rubygems.org'
 
 gem 'faraday', '~> 0.15.4'
 
-gem 'rake', [">= 10.0", "< 12"]
+gem 'rake', ['>= 10.0', '< 12']
 
 gemspec :path => '../'
diff --git a/gemfiles/ruby_1.9.gemfile b/gemfiles/ruby_1.9.gemfile
index bbef7523..276621ef 100644
--- a/gemfiles/ruby_1.9.gemfile
+++ b/gemfiles/ruby_1.9.gemfile
@@ -4,7 +4,7 @@ gem 'faraday', '~> 0.15.4'
 
 gem 'json', '< 2.0'
 gem 'rack', '~> 1.2'
-gem 'rake', [">= 10.0", "< 12"]
+gem 'rake', ['>= 10.0', '< 12']
 gem 'term-ansicolor', '< 1.4.0'
 gem 'tins', '< 1.7'
 
diff --git a/gemfiles/ruby_2.1.gemfile b/gemfiles/ruby_2.1.gemfile
deleted file mode 100644
index 87a679f6..00000000
--- a/gemfiles/ruby_2.1.gemfile
+++ /dev/null
@@ -1,6 +0,0 @@
-source 'https://rubygems.org'
-
-gem 'faraday', '~> 0.15.4'
-gem 'rack', '~> 1.2'
-
-gemspec :path => '../'
diff --git a/gemfiles/ruby_2.3.gemfile b/gemfiles/ruby_2.3.gemfile
deleted file mode 100644
index a02c547f..00000000
--- a/gemfiles/ruby_2.3.gemfile
+++ /dev/null
@@ -1,3 +0,0 @@
-source 'https://rubygems.org'
-
-gemspec :path => '../'
diff --git a/gemfiles/ruby_2.4.gemfile b/gemfiles/ruby_2.4.gemfile
deleted file mode 100644
index a02c547f..00000000
--- a/gemfiles/ruby_2.4.gemfile
+++ /dev/null
@@ -1,3 +0,0 @@
-source 'https://rubygems.org'
-
-gemspec :path => '../'
diff --git a/gemfiles/ruby_2.5.gemfile b/gemfiles/ruby_2.5.gemfile
deleted file mode 100644
index a02c547f..00000000
--- a/gemfiles/ruby_2.5.gemfile
+++ /dev/null
@@ -1,3 +0,0 @@
-source 'https://rubygems.org'
-
-gemspec :path => '../'
diff --git a/gemfiles/ruby_2.6.gemfile b/gemfiles/ruby_2.6.gemfile
deleted file mode 100644
index 822e2f2c..00000000
--- a/gemfiles/ruby_2.6.gemfile
+++ /dev/null
@@ -1,9 +0,0 @@
-source 'https://rubygems.org'
-
-group :development do
-  gem 'pry'
-  gem 'byebug'
-  gem 'pry-byebug'
-end
-
-gemspec :path => '../'
diff --git a/gemfiles/ruby_head.gemfile b/gemfiles/ruby_head.gemfile
index 822e2f2c..c7a3bfd9 100644
--- a/gemfiles/ruby_head.gemfile
+++ b/gemfiles/ruby_head.gemfile
@@ -1,8 +1,8 @@
 source 'https://rubygems.org'
 
 group :development do
-  gem 'pry'
   gem 'byebug'
+  gem 'pry'
   gem 'pry-byebug'
 end
 
diff --git a/gemfiles/ruby_2.2.gemfile b/gemfiles/truffleruby.gemfile
similarity index 100%
rename from gemfiles/ruby_2.2.gemfile
rename to gemfiles/truffleruby.gemfile
diff --git a/lib/oauth2/access_token.rb b/lib/oauth2/access_token.rb
index 1b178390..db8c2239 100644
--- a/lib/oauth2/access_token.rb
+++ b/lib/oauth2/access_token.rb
@@ -3,6 +3,7 @@ class AccessToken
     attr_reader :client, :token, :expires_in, :expires_at, :params
     attr_accessor :options, :refresh_token
 
+    # Should these methods be deprecated?
     class << self
       # Initializes an AccessToken from a Hash
       #
@@ -46,11 +47,11 @@ def initialize(client, token, opts = {}) # rubocop:disable Metrics/AbcSize
       end
       @expires_in ||= opts.delete('expires')
       @expires_in &&= @expires_in.to_i
-      @expires_at &&= @expires_at.to_i
+      @expires_at &&= convert_expires_at(@expires_at)
       @expires_at ||= Time.now.to_i + @expires_in if @expires_in
-      @options = {:mode          => opts.delete(:mode) || :header,
+      @options = {:mode => opts.delete(:mode) || :header,
                   :header_format => opts.delete(:header_format) || 'Bearer %s',
-                  :param_name    => opts.delete(:param_name) || 'access_token'}
+                  :param_name => opts.delete(:param_name) || 'access_token'}
       @params = opts
     end
 
@@ -81,6 +82,7 @@ def expired?
     # @note options should be carried over to the new AccessToken
     def refresh!(params = {})
       raise('A refresh_token is not available') unless refresh_token
+
       params[:grant_type] = 'refresh_token'
       params[:refresh_token] = refresh_token
       new_token = @client.get_token(params)
@@ -149,7 +151,7 @@ def headers
 
   private
 
-    def configure_authentication!(opts) # rubocop:disable MethodLength, Metrics/AbcSize
+    def configure_authentication!(opts) # rubocop:disable Metrics/AbcSize
       case options[:mode]
       when :header
         opts[:headers] ||= {}
@@ -169,5 +171,13 @@ def configure_authentication!(opts) # rubocop:disable MethodLength, Metrics/AbcS
         raise("invalid :mode option of #{options[:mode]}")
       end
     end
+
+    def convert_expires_at(expires_at)
+      expires_at_i = expires_at.to_i
+      return expires_at_i if expires_at_i > Time.now.utc.to_i
+      return Time.parse(expires_at).to_i if expires_at.is_a?(String)
+
+      expires_at_i
+    end
   end
 end
diff --git a/lib/oauth2/authenticator.rb b/lib/oauth2/authenticator.rb
index ce627920..9588da34 100644
--- a/lib/oauth2/authenticator.rb
+++ b/lib/oauth2/authenticator.rb
@@ -25,6 +25,10 @@ def apply(params)
         apply_basic_auth(params)
       when :request_body
         apply_params_auth(params)
+      when :tls_client_auth
+        apply_client_id(params)
+      when :private_key_jwt
+        params
       else
         raise NotImplementedError
       end
@@ -42,6 +46,12 @@ def apply_params_auth(params)
       {'client_id' => id, 'client_secret' => secret}.merge(params)
     end
 
+    # When using schemes that don't require the client_secret to be passed i.e TLS Client Auth,
+    # we don't want to send the secret
+    def apply_client_id(params)
+      {'client_id' => id}.merge(params)
+    end
+
     # Adds an `Authorization` header with Basic Auth credentials if and only if
     # it is not already set in the params.
     def apply_basic_auth(params)
diff --git a/lib/oauth2/client.rb b/lib/oauth2/client.rb
index 356f93e7..f98a9f37 100644
--- a/lib/oauth2/client.rb
+++ b/lib/oauth2/client.rb
@@ -4,6 +4,8 @@
 module OAuth2
   # The OAuth2::Client class
   class Client # rubocop:disable Metrics/ClassLength
+    RESERVED_PARAM_KEYS = %w[headers parse].freeze
+
     attr_reader :id, :secret, :site
     attr_accessor :options
     attr_writer :connection
@@ -23,8 +25,8 @@ class Client # rubocop:disable Metrics/ClassLength
     # @option opts [Symbol] :auth_scheme (:basic_auth) HTTP method to use to authorize request (:basic_auth or :request_body)
     # @option opts [Hash] :connection_opts ({}) Hash of connection options to pass to initialize Faraday with
     # @option opts [FixNum] :max_redirects (5) maximum number of redirects to follow
-    # @option opts [Boolean] :raise_errors (true) whether or not to raise an OAuth2::Error
-    #  on responses with 400+ status codes
+    # @option opts [Boolean] :raise_errors (true) whether or not to raise an OAuth2::Error on responses with 400+ status codes
+    # @option opts [Proc] :extract_access_token  proc that extracts the access token from the response
     # @yield [builder] The Faraday connection builder
     def initialize(client_id, client_secret, options = {}, &block)
       opts = options.dup
@@ -32,14 +34,18 @@ def initialize(client_id, client_secret, options = {}, &block)
       @secret = client_secret
       @site = opts.delete(:site)
       ssl = opts.delete(:ssl)
-      @options = {:authorize_url    => '/oauth/authorize',
-                  :token_url        => '/oauth/token',
-                  :token_method     => :post,
-                  :auth_scheme      => :request_body,
-                  :connection_opts  => {},
-                  :connection_build => block,
-                  :max_redirects    => 5,
-                  :raise_errors     => true}.merge(opts)
+
+      @options = {
+        :authorize_url => '/oauth/authorize',
+        :token_url => '/oauth/token',
+        :token_method => :post,
+        :auth_scheme => :request_body,
+        :connection_opts => {},
+        :connection_build => block,
+        :max_redirects => 5,
+        :raise_errors => true,
+        :extract_access_token => DEFAULT_EXTRACT_ACCESS_TOKEN,
+      }.merge(opts)
       @options[:connection_opts][:ssl] = ssl if ssl
     end
 
@@ -91,12 +97,13 @@ def token_url(params = nil)
     #   code response for this request.  Will default to client option
     # @option opts [Symbol] :parse @see Response::initialize
     # @yield [req] The Faraday request
-    def request(verb, url, opts = {}) # rubocop:disable CyclomaticComplexity, MethodLength, Metrics/AbcSize
+    def request(verb, url, opts = {}) # rubocop:disable Metrics/MethodLength, Metrics/AbcSize
       connection.response :logger, ::Logger.new($stdout) if ENV['OAUTH_DEBUG'] == 'true'
 
-      url = connection.build_url(url, opts[:params]).to_s
+      url = connection.build_url(url).to_s
 
       response = connection.run_request(verb, url, opts[:body], opts[:headers]) do |req|
+        req.params.update(opts[:params]) if opts[:params]
         yield(req) if block_given?
       end
       response = Response.new(response, :parse => opts[:parse])
@@ -106,6 +113,7 @@ def request(verb, url, opts = {}) # rubocop:disable CyclomaticComplexity, Method
         opts[:redirect_count] ||= 0
         opts[:redirect_count] += 1
         return response if opts[:redirect_count] > options[:max_redirects]
+
         if response.status == 303
           verb = :get
           opts.delete(:body)
@@ -117,6 +125,7 @@ def request(verb, url, opts = {}) # rubocop:disable CyclomaticComplexity, Method
       when 400..599
         error = Error.new(response)
         raise(error) if opts.fetch(:raise_errors, options[:raise_errors])
+
         response.error = error
         response
       else
@@ -130,8 +139,17 @@ def request(verb, url, opts = {}) # rubocop:disable CyclomaticComplexity, Method
     # @param [Hash] params a Hash of params for the token endpoint
     # @param [Hash] access token options, to pass to the AccessToken object
     # @param [Class] class of access token for easier subclassing OAuth2::AccessToken
-    # @return [AccessToken] the initalized AccessToken
-    def get_token(params, access_token_opts = {}, access_token_class = AccessToken) # rubocop:disable Metrics/AbcSize, Metrics/MethodLength
+    # @return [AccessToken] the initialized AccessToken
+    def get_token(params, access_token_opts = {}, extract_access_token = options[:extract_access_token]) # rubocop:disable Metrics/AbcSize, Metrics/MethodLength
+      params = params.map do |key, value|
+        if RESERVED_PARAM_KEYS.include?(key)
+          [key.to_sym, value]
+        else
+          [key, value]
+        end
+      end
+      params = Hash[params]
+
       params = Authenticator.new(id, secret, options[:auth_scheme]).apply(params)
       opts = {:raise_errors => options[:raise_errors], :parse => params.delete(:parse)}
       headers = params.delete(:headers) || {}
@@ -144,11 +162,18 @@ def get_token(params, access_token_opts = {}, access_token_class = AccessToken)
       end
       opts[:headers].merge!(headers)
       response = request(options[:token_method], token_url, opts)
-      if options[:raise_errors] && !(response.parsed.is_a?(Hash) && response.parsed['access_token'])
+
+      access_token = begin
+        build_access_token(response, access_token_opts, extract_access_token)
+      rescue StandardError
+        nil
+      end
+
+      if options[:raise_errors] && !access_token
         error = Error.new(response)
         raise(error)
       end
-      access_token_class.from_hash(self, response.parsed.merge(access_token_opts))
+      access_token
     end
 
     # The Authorization Code strategy
@@ -206,5 +231,27 @@ def redirection_params
         {}
       end
     end
+
+    DEFAULT_EXTRACT_ACCESS_TOKEN = proc do |client, hash|
+      token = hash.delete('access_token') || hash.delete(:access_token)
+      token && AccessToken.new(client, token, hash)
+    end
+
+  private
+
+    def build_access_token(response, access_token_opts, extract_access_token)
+      parsed_response = response.parsed.dup
+      return unless parsed_response.is_a?(Hash)
+
+      hash = parsed_response.merge(access_token_opts)
+
+      # Provide backwards compatibility for old AcessToken.form_hash pattern
+      # Should be deprecated in 2.x
+      if extract_access_token.is_a?(Class) && extract_access_token.respond_to?(:from_hash)
+        extract_access_token.from_hash(self, hash)
+      else
+        extract_access_token.call(self, hash)
+      end
+    end
   end
 end
diff --git a/lib/oauth2/mac_token.rb b/lib/oauth2/mac_token.rb
index db7d4d77..99c6f5ec 100644
--- a/lib/oauth2/mac_token.rb
+++ b/lib/oauth2/mac_token.rb
@@ -98,9 +98,17 @@ def algorithm=(alg)
       @algorithm = begin
         case alg.to_s
         when 'hmac-sha-1'
-          OpenSSL::Digest::SHA1.new
+          begin
+            OpenSSL::Digest('SHA1').new
+          rescue StandardError
+            OpenSSL::Digest.new('SHA1')
+          end
         when 'hmac-sha-256'
-          OpenSSL::Digest::SHA256.new
+          begin
+            OpenSSL::Digest('SHA256').new
+          rescue StandardError
+            OpenSSL::Digest.new('SHA256')
+          end
         else
           raise(ArgumentError, 'Unsupported algorithm')
         end
diff --git a/lib/oauth2/response.rb b/lib/oauth2/response.rb
index 13657fd9..fd98617b 100644
--- a/lib/oauth2/response.rb
+++ b/lib/oauth2/response.rb
@@ -11,9 +11,9 @@ class Response
     # Procs that, when called, will parse a response body according
     # to the specified format.
     @@parsers = {
-      :json  => lambda { |body| MultiJson.load(body) rescue body }, # rubocop:disable RescueModifier
+      :json => lambda { |body| MultiJson.load(body) rescue body }, # rubocop:disable Style/RescueModifier
       :query => lambda { |body| Rack::Utils.parse_query(body) },
-      :text  => lambda { |body| body },
+      :text => lambda { |body| body },
     }
 
     # Content type assignments for various potential HTTP content types.
@@ -68,6 +68,7 @@ def body
     #   application/json Content-Type response bodies
     def parsed
       return nil unless @@parsers.key?(parser)
+
       @parsed ||= @@parsers[parser].call(body)
     end
 
@@ -79,11 +80,12 @@ def content_type
     # Determines the parser that will be used to supply the content of #parsed
     def parser
       return options[:parse].to_sym if @@parsers.key?(options[:parse])
+
       @@content_types[content_type]
     end
   end
 end
 
 OAuth2::Response.register_parser(:xml, ['text/xml', 'application/rss+xml', 'application/rdf+xml', 'application/atom+xml']) do |body|
-  MultiXml.parse(body) rescue body # rubocop:disable RescueModifier
+  MultiXml.parse(body) rescue body # rubocop:disable Style/RescueModifier
 end
diff --git a/lib/oauth2/strategy/assertion.rb b/lib/oauth2/strategy/assertion.rb
index b3b577be..8dc27b50 100644
--- a/lib/oauth2/strategy/assertion.rb
+++ b/lib/oauth2/strategy/assertion.rb
@@ -50,10 +50,10 @@ def get_token(params = {}, opts = {})
       def build_request(params)
         assertion = build_assertion(params)
         {
-          :grant_type     => 'assertion',
+          :grant_type => 'assertion',
           :assertion_type => 'urn:ietf:params:oauth:grant-type:jwt-bearer',
-          :assertion      => assertion,
-          :scope          => params[:scope],
+          :assertion => assertion,
+          :scope => params[:scope],
         }
       end
 
diff --git a/lib/oauth2/strategy/password.rb b/lib/oauth2/strategy/password.rb
index 49bfc6e3..075dec51 100644
--- a/lib/oauth2/strategy/password.rb
+++ b/lib/oauth2/strategy/password.rb
@@ -18,8 +18,8 @@ def authorize_url
       # @param [Hash] params additional params
       def get_token(username, password, params = {}, opts = {})
         params = {'grant_type' => 'password',
-                  'username'   => username,
-                  'password'   => password}.merge(params)
+                  'username' => username,
+                  'password' => password}.merge(params)
         @client.get_token(params, opts)
       end
     end
diff --git a/lib/oauth2/version.rb b/lib/oauth2/version.rb
index 6b63a98c..6b7b63e0 100644
--- a/lib/oauth2/version.rb
+++ b/lib/oauth2/version.rb
@@ -1,5 +1,7 @@
 module OAuth2
   module Version
+    VERSION = to_s
+
   module_function
 
     # The major version
@@ -20,7 +22,7 @@ def minor
     #
     # @return [Integer]
     def patch
-      1
+      5
     end
 
     # The pre-release version, if any
diff --git a/maintenance-branch b/maintenance-branch
new file mode 100644
index 00000000..8b25206f
--- /dev/null
+++ b/maintenance-branch
@@ -0,0 +1 @@
+master
\ No newline at end of file
diff --git a/oauth2.gemspec b/oauth2.gemspec
index be52c417..86a825c7 100644
--- a/oauth2.gemspec
+++ b/oauth2.gemspec
@@ -20,7 +20,15 @@ Gem::Specification.new do |spec|
   spec.required_ruby_version = '>= 1.9.0'
   spec.required_rubygems_version = '>= 1.3.5'
   spec.summary       = 'A Ruby wrapper for the OAuth 2.0 protocol.'
-  spec.version       = OAuth2::Version
+  spec.version       = OAuth2::Version.to_s
+
+  spec.metadata = {
+    'bug_tracker_uri' => 'https://github.com/oauth-xx/oauth2/issues',
+    'changelog_uri' => "https://github.com/oauth-xx/oauth2/blob/v#{spec.version}/CHANGELOG.md",
+    'documentation_uri' => "https://www.rubydoc.info/gems/oauth2/#{spec.version}",
+    'source_code_uri' => "https://github.com/oauth-xx/oauth2/tree/v#{spec.version}",
+    'wiki_uri' => 'https://github.com/oauth-xx/oauth2/wiki',
+  }
 
   spec.require_paths = %w[lib]
   spec.bindir        = 'exe'
@@ -36,9 +44,9 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'rake', '~> 12.3'
   spec.add_development_dependency 'rdoc', ['>= 5.0', '< 7']
   spec.add_development_dependency 'rspec', '~> 3.0'
-  spec.add_development_dependency 'rspec-stubbed_env'
-  spec.add_development_dependency 'rspec-pending_for'
   spec.add_development_dependency 'rspec-block_is_expected'
+  spec.add_development_dependency 'rspec-pending_for'
+  spec.add_development_dependency 'rspec-stubbed_env'
   spec.add_development_dependency 'silent_stream'
   spec.add_development_dependency 'wwtd'
 end
diff --git a/spec/helper.rb b/spec/helper.rb
index e3cf4805..8b64d420 100644
--- a/spec/helper.rb
+++ b/spec/helper.rb
@@ -1,6 +1,8 @@
 DEBUG = ENV['DEBUG'] == 'true'
 
-if RUBY_VERSION >= '1.9'
+ruby_version = Gem::Version.new(RUBY_VERSION)
+
+if ruby_version >= Gem::Version.new('2.7')
   require 'simplecov'
   require 'coveralls'
 
@@ -12,9 +14,7 @@
   end
 end
 
-if DEBUG && RUBY_VERSION >= '2.6'
-  require 'byebug'
-end
+require 'byebug' if DEBUG && ruby_version >= Gem::Version.new('2.4')
 
 require 'oauth2'
 require 'addressable/uri'
@@ -30,11 +30,6 @@
 
 Faraday.default_adapter = :test
 
-# This is dangerous - HERE BE DRAGONS.
-# It allows us to refer to classes without the namespace, but at what cost?!?
-# TODO: Refactor to use explicit references everywhere
-include OAuth2
-
 RSpec.configure do |conf|
   conf.include SilentStream
 end
diff --git a/spec/oauth2/access_token_spec.rb b/spec/oauth2/access_token_spec.rb
index ad53b2ac..c586bc4c 100644
--- a/spec/oauth2/access_token_spec.rb
+++ b/spec/oauth2/access_token_spec.rb
@@ -1,17 +1,16 @@
-require 'helper'
-
-describe AccessToken do
+describe OAuth2::AccessToken do
   subject { described_class.new(client, token) }
 
   let(:token) { 'monkey' }
   let(:refresh_body) { MultiJson.encode(:access_token => 'refreshed_foo', :expires_in => 600, :refresh_token => 'refresh_bar') }
   let(:client) do
-    Client.new('abc', 'def', :site => 'https://api.example.com') do |builder|
+    OAuth2::Client.new('abc', 'def', :site => 'https://api.example.com') do |builder|
       builder.request :url_encoded
       builder.adapter :test do |stub|
         VERBS.each do |verb|
           stub.send(verb, '/token/header') { |env| [200, {}, env[:request_headers]['Authorization']] }
           stub.send(verb, "/token/query?access_token=#{token}") { |env| [200, {}, Addressable::URI.parse(env[:url]).query_values['access_token']] }
+          stub.send(verb, '/token/query_string') { |env| [200, {}, CGI.unescape(Addressable::URI.parse(env[:url]).query)] }
           stub.send(verb, '/token/body') { |env| [200, {}, env[:body]] }
         end
         stub.post('/oauth/token') { |env| [200, {'Content-Type' => 'application/json'}, refresh_body] }
@@ -72,10 +71,12 @@ def assert_initialized_token(target) # rubocop:disable Metrics/AbcSize
     end
 
     it 'initializes with a string expires_at' do
-      hash = {:access_token => token, :expires_at => '1361396829', 'foo' => 'bar'}
+      future = Time.now.utc + 100_000
+      hash = {:access_token => token, :expires_at => future.iso8601, 'foo' => 'bar'}
       target = described_class.from_hash(client, hash)
       assert_initialized_token(target)
       expect(target.expires_at).to be_a(Integer)
+      expect(target.expires_at).to eql(future.to_i)
     end
   end
 
@@ -101,6 +102,11 @@ def assert_initialized_token(target) # rubocop:disable Metrics/AbcSize
         it "sends the token in the Authorization header for a #{verb.to_s.upcase} request" do
           expect(subject.post('/token/query').body).to eq(token)
         end
+
+        it "sends a #{verb.to_s.upcase} request and options[:param_name] include [number]." do
+          subject.options[:param_name] = 'auth[1]'
+          expect(subject.__send__(verb, '/token/query_string').body).to include("auth[1]=#{token}")
+        end
       end
     end
 
@@ -115,6 +121,14 @@ def assert_initialized_token(target) # rubocop:disable Metrics/AbcSize
         end
       end
     end
+
+    context 'params include [number]' do
+      VERBS.each do |verb|
+        it "sends #{verb.to_s.upcase} correct query" do
+          expect(subject.__send__(verb, '/token/query_string', :params => {'foo[bar][1]' => 'val'}).body).to include('foo[bar][1]=val')
+        end
+      end
+    end
   end
 
   describe '#expires?' do
@@ -151,8 +165,8 @@ def assert_initialized_token(target) # rubocop:disable Metrics/AbcSize
   describe '#refresh!' do
     let(:access) do
       described_class.new(client, token, :refresh_token => 'abaca',
-                                         :expires_in     => 600,
-                                         :param_name     => 'o_param')
+                                         :expires_in => 600,
+                                         :param_name => 'o_param')
     end
 
     it 'returns a refresh token with appropriate values carried over' do
diff --git a/spec/oauth2/authenticator_spec.rb b/spec/oauth2/authenticator_spec.rb
index 49838da3..48cbac9b 100644
--- a/spec/oauth2/authenticator_spec.rb
+++ b/spec/oauth2/authenticator_spec.rb
@@ -1,5 +1,3 @@
-require 'helper'
-
 describe OAuth2::Authenticator do
   subject do
     described_class.new(client_id, client_secret, mode)
@@ -38,6 +36,24 @@
           :headers => {'A' => 'b'}
         )
       end
+
+      context 'using tls client authentication' do
+        let(:mode) { :tls_client_auth }
+
+        it 'does not add client_secret' do
+          output = subject.apply({})
+          expect(output).to eq('client_id' => 'foo')
+        end
+      end
+
+      context 'using private key jwt authentication' do
+        let(:mode) { :private_key_jwt }
+
+        it 'does not add client_secret or client_id' do
+          output = subject.apply({})
+          expect(output).to eq({})
+        end
+      end
     end
 
     context 'with Basic authentication' do
diff --git a/spec/oauth2/client_spec.rb b/spec/oauth2/client_spec.rb
index 464a5b5a..583ea12f 100644
--- a/spec/oauth2/client_spec.rb
+++ b/spec/oauth2/client_spec.rb
@@ -157,6 +157,68 @@
         client.auth_code.get_token('code')
       end
     end
+
+    describe 'custom headers' do
+      context 'string key headers' do
+        it 'adds the custom headers to request' do
+          client = described_class.new('abc', 'def', :site => 'https://api.example.com', :auth_scheme => :request_body) do |builder|
+            builder.adapter :test do |stub|
+              stub.post('/oauth/token') do |env|
+                expect(env.request_headers).to include({'CustomHeader' => 'CustomHeader'})
+                [200, {'Content-Type' => 'application/json'}, '{"access_token":"token"}']
+              end
+            end
+          end
+          header_params = {'headers' => {'CustomHeader' => 'CustomHeader'}}
+          client.auth_code.get_token('code', header_params)
+        end
+      end
+
+      context 'symbol key headers' do
+        it 'adds the custom headers to request' do
+          client = described_class.new('abc', 'def', :site => 'https://api.example.com', :auth_scheme => :request_body) do |builder|
+            builder.adapter :test do |stub|
+              stub.post('/oauth/token') do |env|
+                expect(env.request_headers).to include({'CustomHeader' => 'CustomHeader'})
+                [200, {'Content-Type' => 'application/json'}, '{"access_token":"token"}']
+              end
+            end
+          end
+          header_params = {:headers => {'CustomHeader' => 'CustomHeader'}}
+          client.auth_code.get_token('code', header_params)
+        end
+      end
+
+      context 'string key custom headers with basic auth' do
+        it 'adds the custom headers to request' do
+          client = described_class.new('abc', 'def', :site => 'https://api.example.com') do |builder|
+            builder.adapter :test do |stub|
+              stub.post('/oauth/token') do |env|
+                expect(env.request_headers).to include({'CustomHeader' => 'CustomHeader'})
+                [200, {'Content-Type' => 'application/json'}, '{"access_token":"token"}']
+              end
+            end
+          end
+          header_params = {'headers' => {'CustomHeader' => 'CustomHeader'}}
+          client.auth_code.get_token('code', header_params)
+        end
+      end
+
+      context 'symbol key custom headers with basic auth' do
+        it 'adds the custom headers to request' do
+          client = described_class.new('abc', 'def', :site => 'https://api.example.com') do |builder|
+            builder.adapter :test do |stub|
+              stub.post('/oauth/token') do |env|
+                expect(env.request_headers).to include({'CustomHeader' => 'CustomHeader'})
+                [200, {'Content-Type' => 'application/json'}, '{"access_token":"token"}']
+              end
+            end
+          end
+          header_params = {:headers => {'CustomHeader' => 'CustomHeader'}}
+          client.auth_code.get_token('code', header_params)
+        end
+      end
+    end
   end
 
   describe '#request' do
@@ -212,12 +274,13 @@
       end
     end
 
+    # rubocop:disable Style/RedundantBegin
     it 're-encodes response body in the error message' do
       begin
         subject.request(:get, '/ascii_8bit_encoding')
-      rescue StandardError => ex
-        expect(ex.message.encoding.name).to eq('UTF-8')
-        expect(ex.message).to eq("invalid_request: é\n{\"error\":\"invalid_request\",\"error_description\":\"��\"}")
+      rescue StandardError => e
+        expect(e.message.encoding.name).to eq('UTF-8')
+        expect(e.message).to eq("invalid_request: é\n{\"error\":\"invalid_request\",\"error_description\":\"��\"}")
       end
     end
 
@@ -240,20 +303,22 @@
         expect(e.to_s).to match(/unknown error/)
       end
     end
+    # rubocop:enable Style/RedundantBegin
 
     context 'with ENV' do
       include_context 'with stubbed env'
       before do
         stub_env('OAUTH_DEBUG' => 'true')
       end
+
       it 'outputs to $stdout when OAUTH_DEBUG=true' do
         output = capture(:stdout) do
           subject.request(:get, '/success')
         end
         logs = [
-          'INFO -- request: GET https://api.example.com/success',
-          'INFO -- response: Status 200',
-          'DEBUG -- response: Content-Type: "text/awesome"'
+          '-- request: GET https://api.example.com/success',
+          '-- response: Status 200',
+          '-- response: Content-Type: "text/awesome"',
         ]
         expect(output).to include(*logs)
       end
@@ -286,12 +351,129 @@
       client = stubbed_client(:auth_scheme => :basic_auth) do |stub|
         stub.post('/oauth/token') do |env|
           raise Faraday::Adapter::Test::Stubs::NotFound unless env[:request_headers]['Authorization'] == OAuth2::Authenticator.encode_basic_auth('abc', 'def')
+
           [200, {'Content-Type' => 'application/json'}, MultiJson.encode('access_token' => 'the-token')]
         end
       end
       client.get_token({})
     end
 
+    describe 'extract_access_token option' do
+      let(:client) do
+        client = stubbed_client(:extract_access_token => extract_access_token) do |stub|
+          stub.post('/oauth/token') do
+            [200, {'Content-Type' => 'application/json'}, MultiJson.encode('data' => {'access_token' => 'the-token'})]
+          end
+        end
+      end
+
+      context 'with proc extract_access_token' do
+        let(:extract_access_token) do
+          proc do |client, hash|
+            token = hash['data']['access_token']
+            OAuth2::AccessToken.new(client, token, hash)
+          end
+        end
+
+        it 'returns a configured AccessToken' do
+          token = client.get_token({})
+          expect(token).to be_a OAuth2::AccessToken
+          expect(token.token).to eq('the-token')
+        end
+      end
+
+      context 'with depracted Class.from_hash option' do
+        let(:extract_access_token) do
+          CustomAccessToken = Class.new(OAuth2::AccessToken)
+          CustomAccessToken.define_singleton_method(:from_hash) do |client, hash|
+            token = hash['data']['access_token']
+            OAuth2::AccessToken.new(client, token, hash)
+          end
+          CustomAccessToken
+        end
+
+        it 'returns a configured AccessToken' do
+          token = client.get_token({})
+          expect(token).to be_a OAuth2::AccessToken
+          expect(token.token).to eq('the-token')
+        end
+      end
+    end
+
+    describe ':raise_errors flag' do
+      let(:options) { {} }
+      let(:token_response) { nil }
+
+      let(:client) do
+        stubbed_client(options.merge(:raise_errors => raise_errors)) do |stub|
+          stub.post('/oauth/token') do
+            # stub 200 response so that we're testing the get_token handling of :raise_errors flag not request
+            [200, {'Content-Type' => 'application/json'}, token_response]
+          end
+        end
+      end
+
+      context 'when set to false' do
+        let(:raise_errors) { false }
+
+        context 'when the request body is nil' do
+          it 'returns a nil :access_token' do
+            expect(client.get_token({})).to eq(nil)
+          end
+        end
+
+        context 'when the request body is missing the access_token' do
+          let(:token_response) { MultiJson.encode('unexpected_access_token' => 'the-token') }
+
+          it 'returns a nil :access_token' do
+            expect(client.get_token({})).to eq(nil)
+          end
+        end
+
+        context 'when extract_access_token raises an exception' do
+          let(:options) do
+            {
+              :extract_access_token => proc { |client, hash| raise ArgumentError },
+            }
+          end
+
+          it 'returns a nil :access_token' do
+            expect(client.get_token({})).to eq(nil)
+          end
+        end
+      end
+
+      context 'when set to true' do
+        let(:raise_errors) { true }
+
+        context 'when the request body is nil' do
+          it 'raises an error' do
+            expect { client.get_token({}) }.to raise_error OAuth2::Error
+          end
+        end
+
+        context 'when the request body is missing the access_token' do
+          let(:token_response) { MultiJson.encode('unexpected_access_token' => 'the-token') }
+
+          it 'raises an error' do
+            expect { client.get_token({}) }.to raise_error OAuth2::Error
+          end
+        end
+
+        context 'when extract_access_token raises an exception' do
+          let(:options) do
+            {
+              :extract_access_token => proc { |client, hash| raise ArgumentError },
+            }
+          end
+
+          it 'raises an error' do
+            expect { client.get_token({}) }.to raise_error OAuth2::Error
+          end
+        end
+      end
+    end
+
     def stubbed_client(params = {}, &stubs)
       params = {:site => 'https://api.example.com'}.merge(params)
       OAuth2::Client.new('abc', 'def', params) do |builder|
diff --git a/spec/oauth2/mac_token_spec.rb b/spec/oauth2/mac_token_spec.rb
index add5f72e..0685350f 100644
--- a/spec/oauth2/mac_token_spec.rb
+++ b/spec/oauth2/mac_token_spec.rb
@@ -1,11 +1,9 @@
-require 'helper'
-
-describe MACToken do
+describe OAuth2::MACToken do
   subject { described_class.new(client, token, 'abc123') }
 
   let(:token) { 'monkey' }
   let(:client) do
-    Client.new('abc', 'def', :site => 'https://api.example.com') do |builder|
+    OAuth2::Client.new('abc', 'def', :site => 'https://api.example.com') do |builder|
       builder.request :url_encoded
       builder.adapter :test do |stub|
         VERBS.each do |verb|
@@ -91,7 +89,7 @@
     subject { described_class.from_access_token(access_token, 'hello') }
 
     let(:access_token) do
-      AccessToken.new(
+      OAuth2::AccessToken.new(
         client, token,
         :expires_at => 1,
         :expires_in => 1,
diff --git a/spec/oauth2/response_spec.rb b/spec/oauth2/response_spec.rb
index ace9ac52..3171fd26 100644
--- a/spec/oauth2/response_spec.rb
+++ b/spec/oauth2/response_spec.rb
@@ -1,5 +1,3 @@
-require 'helper'
-
 describe OAuth2::Response do
   describe '#initialize' do
     let(:status) { 200 }
@@ -8,9 +6,9 @@
 
     it 'returns the status, headers and body' do
       response = double('response', :headers => headers,
-                                    :status  => status,
-                                    :body    => body)
-      subject = Response.new(response)
+                                    :status => status,
+                                    :body => body)
+      subject = described_class.new(response)
       expect(subject.headers).to eq(headers)
       expect(subject.status).to eq(status)
       expect(subject.body).to eq(body)
@@ -45,7 +43,7 @@
       headers = {'Content-Type' => 'application/x-www-form-urlencoded'}
       body = 'foo=bar&answer=42'
       response = double('response', :headers => headers, :body => body)
-      subject = Response.new(response)
+      subject = described_class.new(response)
       expect(subject.parsed.keys.size).to eq(2)
       expect(subject.parsed['foo']).to eq('bar')
       expect(subject.parsed['answer']).to eq('42')
@@ -55,7 +53,7 @@
       headers = {'Content-Type' => 'application/json'}
       body = MultiJson.encode(:foo => 'bar', :answer => 42)
       response = double('response', :headers => headers, :body => body)
-      subject = Response.new(response)
+      subject = described_class.new(response)
       expect(subject.parsed.keys.size).to eq(2)
       expect(subject.parsed['foo']).to eq('bar')
       expect(subject.parsed['answer']).to eq(42)
@@ -71,7 +69,7 @@
       expect(MultiJson).not_to receive(:load)
       expect(Rack::Utils).not_to receive(:parse_query)
 
-      subject = Response.new(response)
+      subject = described_class.new(response)
       expect(subject.parsed).to be_nil
     end
   end
diff --git a/spec/oauth2/strategy/assertion_spec.rb b/spec/oauth2/strategy/assertion_spec.rb
index 36ea17de..148e3e3a 100644
--- a/spec/oauth2/strategy/assertion_spec.rb
+++ b/spec/oauth2/strategy/assertion_spec.rb
@@ -1,5 +1,3 @@
-require 'helper'
-
 describe OAuth2::Strategy::Assertion do
   subject { client.assertion }
 
@@ -22,8 +20,8 @@
 
   let(:params) do
     {
-        :hmac_secret => 'foo',
-        :exp => Time.now.utc.to_i + 3600
+      :hmac_secret => 'foo',
+      :exp => Time.now.utc.to_i + 3600,
     }
   end
 
diff --git a/spec/oauth2/strategy/auth_code_spec.rb b/spec/oauth2/strategy/auth_code_spec.rb
index bcb1984f..36cd3a5a 100644
--- a/spec/oauth2/strategy/auth_code_spec.rb
+++ b/spec/oauth2/strategy/auth_code_spec.rb
@@ -1,7 +1,5 @@
 # encoding: utf-8
 
-require 'helper'
-
 describe OAuth2::Strategy::AuthCode do
   subject { client.auth_code }
 
diff --git a/spec/oauth2/strategy/base_spec.rb b/spec/oauth2/strategy/base_spec.rb
index fb59e963..67c66d1a 100644
--- a/spec/oauth2/strategy/base_spec.rb
+++ b/spec/oauth2/strategy/base_spec.rb
@@ -1,5 +1,3 @@
-require 'helper'
-
 describe OAuth2::Strategy::Base do
   it 'initializes with a Client' do
     expect { described_class.new(OAuth2::Client.new('abc', 'def')) }.not_to raise_error
diff --git a/spec/oauth2/strategy/client_credentials_spec.rb b/spec/oauth2/strategy/client_credentials_spec.rb
index 11d3b525..4f91bfd5 100644
--- a/spec/oauth2/strategy/client_credentials_spec.rb
+++ b/spec/oauth2/strategy/client_credentials_spec.rb
@@ -1,5 +1,3 @@
-require 'helper'
-
 describe OAuth2::Strategy::ClientCredentials do
   subject { client.client_credentials }
 
diff --git a/spec/oauth2/strategy/implicit_spec.rb b/spec/oauth2/strategy/implicit_spec.rb
index 7f48ec04..c4df8ebd 100644
--- a/spec/oauth2/strategy/implicit_spec.rb
+++ b/spec/oauth2/strategy/implicit_spec.rb
@@ -1,5 +1,3 @@
-require 'helper'
-
 describe OAuth2::Strategy::Implicit do
   subject { client.implicit }
 
diff --git a/spec/oauth2/strategy/password_spec.rb b/spec/oauth2/strategy/password_spec.rb
index 0c9a07dd..c8b006aa 100644
--- a/spec/oauth2/strategy/password_spec.rb
+++ b/spec/oauth2/strategy/password_spec.rb
@@ -1,5 +1,3 @@
-require 'helper'
-
 describe OAuth2::Strategy::Password do
   subject { client.password }
 
diff --git a/spec/oauth2/version_spec.rb b/spec/oauth2/version_spec.rb
new file mode 100644
index 00000000..3e395eac
--- /dev/null
+++ b/spec/oauth2/version_spec.rb
@@ -0,0 +1,5 @@
+describe OAuth2::Version do
+  it 'VERSION a sting' do
+    expect(OAuth2::Version::VERSION).to be_a(String)
+  end
+end