diff --git a/.rubocop.yml b/.rubocop.yml
index cf2c4b76..03f24c50 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -15,5 +15,3 @@ Metrics/ModuleLength:
 Metrics/BlockLength:
   Exclude:
     - "googleauth.gemspec"
-Style/SafeNavigation:
-  Enabled: false
diff --git a/Gemfile b/Gemfile
index 0d9f6c1a..2d3b11b3 100755
--- a/Gemfile
+++ b/Gemfile
@@ -8,7 +8,7 @@ group :development do
   gem "coveralls", "~> 0.7"
   gem "fakefs", "~> 0.6"
   gem "fakeredis", "~> 0.5"
-  gem "google-style", "~> 1.24.0"
+  gem "google-style", "~> 1.25.1"
   gem "logging", "~> 2.0"
   gem "minitest", "~> 5.14"
   gem "minitest-focus", "~> 1.1"
@@ -21,10 +21,5 @@ group :development do
   gem "webmock", "~> 3.8"
 end
 
-platforms :jruby do
-  group :development do
-  end
-end
-
-gem "faraday", "~> 0.17"
+gem "faraday", ">= 0.17.3", "< 2.0"
 gem "gems", "~> 1.2"
diff --git a/README.md b/README.md
index 5eb3ec94..029b5aa3 100644
--- a/README.md
+++ b/README.md
@@ -182,12 +182,14 @@ Custom storage implementations can also be used. See
 
 ## Supported Ruby Versions
 
-This library requires Ruby 2.4 or later.
-
-In general, this library supports Ruby versions that are considered current and
-supported by Ruby Core (that is, Ruby versions that are either in normal
-maintenance or in security maintenance).
-See https://www.ruby-lang.org/en/downloads/branches/ for further details.
+This library is supported on Ruby 2.5+.
+
+Google provides official support for Ruby versions that are actively supported
+by Ruby Core—that is, Ruby versions that are either in normal maintenance or in
+security maintenance, and not end of life. Currently, this means Ruby 2.5 and
+later. Older versions of Ruby _may_ still work, but are unsupported and not
+recommended. See https://www.ruby-lang.org/en/downloads/branches/ for details
+about the Ruby support schedule.
 
 ## License
 
diff --git a/googleauth.gemspec b/googleauth.gemspec
index 74fb9b60..6a4bf1be 100755
--- a/googleauth.gemspec
+++ b/googleauth.gemspec
@@ -24,8 +24,9 @@ Gem::Specification.new do |gem|
     File.basename f
   end
   gem.require_paths = ["lib"]
+
   gem.platform      = Gem::Platform::RUBY
-  gem.required_ruby_version = ">= 2.4.0"
+  gem.required_ruby_version = ">= 2.5"
 
   gem.add_dependency "faraday", ">= 0.17.3", "< 2.0"
   gem.add_dependency "jwt", ">= 1.4", "< 3.0"
diff --git a/lib/googleauth/credentials.rb b/lib/googleauth/credentials.rb
index bc358845..12f2e020 100644
--- a/lib/googleauth/credentials.rb
+++ b/lib/googleauth/credentials.rb
@@ -369,9 +369,10 @@ def initialize keyfile, options = {}
         verify_keyfile_provided! keyfile
         @project_id = options["project_id"] || options["project"]
         @quota_project_id = options["quota_project_id"]
-        if keyfile.is_a? Signet::OAuth2::Client
+        case keyfile
+        when Signet::OAuth2::Client
           update_from_signet keyfile
-        elsif keyfile.is_a? Hash
+        when Hash
           update_from_hash keyfile, options
         else
           update_from_filepath keyfile, options
@@ -503,9 +504,11 @@ def init_client keyfile, connection_options = {}
 
       # returns a new Hash with string keys instead of symbol keys.
       def stringify_hash_keys hash
-        Hash[hash.map { |k, v| [k.to_s, v] }]
+        hash.to_h.transform_keys(&:to_s)
       end
 
+      # rubocop:disable Metrics/AbcSize
+
       def client_options options
         # Keyfile options have higher priority over constructor defaults
         options["token_credential_uri"] ||= self.class.token_credential_uri
@@ -527,6 +530,8 @@ def client_options options
           signing_key:          OpenSSL::PKey::RSA.new(options["private_key"]) }
       end
 
+      # rubocop:enable Metrics/AbcSize
+
       def update_from_signet client
         @project_id ||= client.project_id if client.respond_to? :project_id
         @quota_project_id ||= client.quota_project_id if client.respond_to? :quota_project_id
diff --git a/lib/googleauth/credentials_loader.rb b/lib/googleauth/credentials_loader.rb
index 79bee2cf..5ecda5d2 100644
--- a/lib/googleauth/credentials_loader.rb
+++ b/lib/googleauth/credentials_loader.rb
@@ -103,7 +103,7 @@ def from_env scope = nil, options = {}
             return make_creds options.merge(json_key_io: f)
           end
         elsif service_account_env_vars? || authorized_user_env_vars?
-          return make_creds options
+          make_creds options
         end
       rescue StandardError => e
         raise "#{NOT_FOUND_ERROR}: #{e}"
diff --git a/lib/googleauth/iam.rb b/lib/googleauth/iam.rb
index 606f357b..8b0b1f0a 100644
--- a/lib/googleauth/iam.rb
+++ b/lib/googleauth/iam.rb
@@ -68,7 +68,7 @@ def apply a_hash
       # Returns a reference to the #apply method, suitable for passing as
       # a closure
       def updater_proc
-        lambda(&method(:apply))
+        proc { |a_hash, _opts = {}| apply a_hash }
       end
     end
   end
diff --git a/lib/googleauth/id_tokens/key_sources.rb b/lib/googleauth/id_tokens/key_sources.rb
index 3a073418..408779ca 100644
--- a/lib/googleauth/id_tokens/key_sources.rb
+++ b/lib/googleauth/id_tokens/key_sources.rb
@@ -171,7 +171,9 @@ def extract_ec_key jwk
             curve_name = CURVE_NAME_MAP[jwk[:crv]]
             raise KeySourceError, "Unsupported EC curve #{jwk[:crv]}" unless curve_name
             group = OpenSSL::PKey::EC::Group.new curve_name
-            bn = OpenSSL::BN.new ["04" + x_data.unpack1("H*") + y_data.unpack1("H*")].pack("H*"), 2
+            x_hex = x_data.unpack1 "H*"
+            y_hex = y_data.unpack1 "H*"
+            bn = OpenSSL::BN.new ["04#{x_hex}#{y_hex}"].pack("H*"), 2
             key = OpenSSL::PKey::EC.new curve_name
             key.public_key = OpenSSL::PKey::EC::Point.new group, bn
             key
@@ -284,10 +286,10 @@ def refresh_keys
             raise KeySourceError, "Unable to retrieve data from #{uri}" unless response.is_a? Net::HTTPSuccess
 
             data = begin
-                     JSON.parse response.body
-                   rescue JSON::ParserError
-                     raise KeySourceError, "Unable to parse JSON"
-                   end
+              JSON.parse response.body
+            rescue JSON::ParserError
+              raise KeySourceError, "Unable to parse JSON"
+            end
 
             @current_keys = Array(interpret_json(data))
           end
diff --git a/lib/googleauth/id_tokens/verifier.rb b/lib/googleauth/id_tokens/verifier.rb
index 4e0a8109..0ba67624 100644
--- a/lib/googleauth/id_tokens/verifier.rb
+++ b/lib/googleauth/id_tokens/verifier.rb
@@ -105,15 +105,13 @@ def verify token,
         def decode_token token, keys, aud, azp, iss
           payload = nil
           keys.find do |key|
-            begin
-              options = { algorithms: key.algorithm }
-              decoded_token = JWT.decode token, key.key, true, options
-              payload = decoded_token.first
-            rescue JWT::ExpiredSignature
-              raise ExpiredTokenError, "Token signature is expired"
-            rescue JWT::DecodeError
-              nil # Try the next key
-            end
+            options = { algorithms: key.algorithm }
+            decoded_token = JWT.decode token, key.key, true, options
+            payload = decoded_token.first
+          rescue JWT::ExpiredSignature
+            raise ExpiredTokenError, "Token signature is expired"
+          rescue JWT::DecodeError
+            nil # Try the next key
           end
 
           normalize_and_verify_payload payload, aud, azp, iss
diff --git a/lib/googleauth/scope_util.rb b/lib/googleauth/scope_util.rb
index c3f03052..17f1bab9 100644
--- a/lib/googleauth/scope_util.rb
+++ b/lib/googleauth/scope_util.rb
@@ -51,7 +51,7 @@ def self.as_array scope
         when Array
           scope
         when String
-          scope.split " "
+          scope.split
         else
           raise "Invalid scope value. Must be string or array"
         end
diff --git a/lib/googleauth/service_account.rb b/lib/googleauth/service_account.rb
index 09cfa46e..dbedf4a1 100644
--- a/lib/googleauth/service_account.rb
+++ b/lib/googleauth/service_account.rb
@@ -203,7 +203,7 @@ def apply a_hash, opts = {}
       # Returns a reference to the #apply method, suitable for passing as
       # a closure
       def updater_proc
-        lambda(&method(:apply))
+        proc { |a_hash, opts = {}| apply a_hash, opts }
       end
 
       protected
diff --git a/lib/googleauth/signet.rb b/lib/googleauth/signet.rb
index d2b33ff0..b8298c51 100644
--- a/lib/googleauth/signet.rb
+++ b/lib/googleauth/signet.rb
@@ -63,7 +63,7 @@ def apply a_hash, opts = {}
       # Returns a reference to the #apply method, suitable for passing as
       # a closure
       def updater_proc
-        lambda(&method(:apply))
+        proc { |a_hash, opts = {}| apply a_hash, opts }
       end
 
       def on_refresh &block
diff --git a/lib/googleauth/stores/file_token_store.rb b/lib/googleauth/stores/file_token_store.rb
index a2268e36..a4838192 100644
--- a/lib/googleauth/stores/file_token_store.rb
+++ b/lib/googleauth/stores/file_token_store.rb
@@ -40,6 +40,7 @@ class FileTokenStore < Google::Auth::TokenStore
         # @param [String, File] file
         #  Path to storage file
         def initialize options = {}
+          super()
           path = options[:file]
           @store = YAML::Store.new path
         end
diff --git a/lib/googleauth/stores/redis_token_store.rb b/lib/googleauth/stores/redis_token_store.rb
index 0a8aef24..72f1b2ef 100644
--- a/lib/googleauth/stores/redis_token_store.rb
+++ b/lib/googleauth/stores/redis_token_store.rb
@@ -49,6 +49,7 @@ class RedisTokenStore < Google::Auth::TokenStore
         #  the options passed through. You may include any other keys accepted
         #  by `Redis.new`
         def initialize options = {}
+          super()
           redis = options.delete :redis
           prefix = options.delete :prefix
           @redis = case redis
diff --git a/lib/googleauth/web_user_authorizer.rb b/lib/googleauth/web_user_authorizer.rb
index 7fb9d4d7..d5b3c7ce 100644
--- a/lib/googleauth/web_user_authorizer.rb
+++ b/lib/googleauth/web_user_authorizer.rb
@@ -189,7 +189,7 @@ def get_authorization_url options = {}
       #  May raise an error if an authorization code is present in the session
       #  and exchange of the code fails
       def get_credentials user_id, request = nil, scope = nil
-        if request && request.session.key?(CALLBACK_STATE_KEY)
+        if request&.session&.key? CALLBACK_STATE_KEY
           # Note - in theory, no need to check required scope as this is
           # expected to be called immediately after a return from authorization
           state_json = request.session.delete CALLBACK_STATE_KEY