Added some more comments

lib/api/api_guard.rb

@@ -139,13 +139,14 @@ module API
     # Exceptions
     #
 
-    MissingTokenError = Class.new(StandardError)
-    TokenNotFoundError = Class.new(StandardError)
-    ExpiredError = Class.new(StandardError)
-    RevokedError = Class.new(StandardError)
-    UnauthorizedError = Class.new(StandardError)
-
-    class InsufficientScopeError < StandardError
+    AuthenticationException = Class.new(StandardError)
+    MissingTokenError = Class.new(AuthenticationException)
+    TokenNotFoundError = Class.new(AuthenticationException)
+    ExpiredError = Class.new(AuthenticationException)
+    RevokedError = Class.new(AuthenticationException)
+    UnauthorizedError = Class.new(AuthenticationException)
+
+    class InsufficientScopeError < AuthenticationException
       attr_reader :scopes
       def initialize(scopes)
         @scopes = scopes.map { |s| s.try(:name) || s }

lib/gitlab/auth/request_authenticator.rb

@@ -17,7 +17,7 @@ module Gitlab
 
       def find_sessionless_user
         find_user_from_access_token || find_user_from_rss_token
-      rescue StandardError
+      rescue API::APIGuard::AuthenticationException
         nil
       end
     end

lib/gitlab/auth/user_auth_finders.rb

@@ -47,13 +47,11 @@ module Gitlab
         @access_token = find_oauth_access_token || find_personal_access_token
       end
 
-      def private_token
-        current_request.params[PRIVATE_TOKEN_PARAM].presence ||
+      def find_personal_access_token
+        token =
+          current_request.params[PRIVATE_TOKEN_PARAM].presence ||
           current_request.env[PRIVATE_TOKEN_HEADER].presence
-      end
 
-      def find_personal_access_token
-        token = private_token
         return unless token
 
         # Expiration, revocation and scopes are verified in `validate_access_token!`
@@ -66,7 +64,7 @@ module Gitlab
 
         # Expiration, revocation and scopes are verified in `validate_access_token!`
         oauth_token = OauthAccessToken.by_token(token)
-        raise(API::APIGuard::UnauthorizedError) unless oauth_token
+        raise API::APIGuard::UnauthorizedError  unless oauth_token
 
         oauth_token.revoke_previous_refresh_token!
         oauth_token

spec/lib/gitlab/auth/request_authenticator_spec.rb

@@ -58,7 +58,7 @@ describe Gitlab::Auth::RequestAuthenticator do
       expect(subject.find_sessionless_user).to be_blank
     end
 
-    it 'rescue StandardError exceptions' do
+    it 'rescue API::APIGuard::AuthenticationException exceptions' do
       allow_any_instance_of(described_class).to receive(:find_user_from_access_token).and_raise(API::APIGuard::UnauthorizedError)
 
       expect(subject.find_sessionless_user).to be_blank