try with Sinatra logger

lib/travis/api/app/base.rb

@@ -1,16 +1,41 @@
 require 'sinatra/base'
+require 'sinatra/custom_logger'
 require 'appsignal/integrations/sinatra' if ENV['APPSIGNAL_ENABLED_FOR_DYNOS']&.split(' ')&.include?(ENV['DYNO'])
 require 'mustermann'
 require 'travis/api/app'
 require 'travis/api/app/extensions'
 require 'travis/api/app/helpers'
+require 'logger'
+
+class CensoredLogger < ::Logger
+  def info(message)
+    super(censor(message))
+  end
+
+  def error(message)
+    super(censor(message))
+  end
+
+  def warn(message)
+    super(censor(message))
+  end
+
+  private
+
+  def censor(message)
+    regex = /token="?'?\w+"?'?/
+    '[censored] ' + message.gsub(regex, 'token=<***>')
+  end
+end
+
 
 class Travis::Api::App
   # Superclass for any endpoint and middleware.
   # Pulls in relevant helpers and extensions.
   class Base < Sinatra::Base
     register Extensions::SmartConstants
     register Mustermann
+    helpers Sinatra::CustomLogger
 
     error NotImplementedError do
       content_type :txt
@@ -50,6 +75,8 @@ def call(env)
         disable  :logging, :dump_errors
       end
 
+      logger = CensoredLogger.new(File.open('/var/log/travis.log', 'a'))
+      set :logger, logger
       register :subclass_tracker, :expose_pattern
       helpers  :respond_with, :mime_types
     end