FEATURE: Add detailed OAuth2 request and response logs

This makes use of Faraday middleware to log precise details about all requests made by the OAuth2 gem. This should make it easier to debug configuration issues

plugin.rb

@@ -46,6 +46,34 @@ class ::OmniAuth::Strategies::Oauth2Basic < ::OmniAuth::Strategies::OAuth2
   end
 end
 
+
+if Gem::Version.new(Faraday::VERSION) > Gem::Version.new('1.0')
+  require 'faraday/logging/formatter'
+  class OAuth2FaradayFormatter < Faraday::Logging::Formatter
+    def request(env)
+      warn <<~LOG
+        OAuth2 Debugging: request #{env.method.upcase} #{env.url.to_s}
+
+        Headers: #{env.request_headers}
+
+        Body: #{env[:body]}
+      LOG
+    end
+    
+    def response(env)
+      warn <<~LOG
+        OAuth2 Debugging: response status #{env.status} 
+        
+        From #{env.method.upcase} #{env.url.to_s}
+
+        Headers: #{env.response_headers}
+
+        Body: #{env[:body]}
+      LOG
+    end
+  end
+end
+
 class ::OAuth2BasicAuthenticator < Auth::ManagedAuthenticator
   def name
     'oauth2_basic'
@@ -80,6 +108,16 @@ class ::OAuth2BasicAuthenticator < Auth::ManagedAuthenticator
                         unless SiteSetting.oauth2_scope.blank?
                           opts[:scope] = SiteSetting.oauth2_scope
                         end
+
+                        if SiteSetting.oauth2_debug_auth && defined? OAuth2FaradayFormatter
+                          opts[:client_options][:connection_build] = lambda{ |builder|
+                            builder.response :logger, Rails.logger, { bodies: true, formatter: OAuth2FaradayFormatter }
+
+                            # Default stack:
+                            builder.request :url_encoded             # form-encode POST params
+                            builder.adapter Faraday.default_adapter  # make requests with Net::HTTP
+                          }
+                        end
                       }
   end