diff --git a/config/locales/en.yml b/config/locales/en.yml
index 254e3f1072..73bcbd49db 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -2688,6 +2688,5 @@ en:
       By default, OpenProject provides OAuth 2.0 authorization via %{authorization_code_flow_link}.
       You can optionally enable %{client_credentials_flow_link}, but you must provide a user on whose behalf requests will be performed.
     authorization_error: "An authorization error has occurred."
-    authorization_error_client_credentials: "Client credentials flow is not allowed for this application."
     revoke_my_application_confirmation: "Do you really want to remove this application? This will revoke %{token_count} active for it."
     my_registered_applications: "Registered OAuth applications"
diff --git a/lib/open_project/authentication/strategies/warden/doorkeeper_oauth.rb b/lib/open_project/authentication/strategies/warden/doorkeeper_oauth.rb
index 1df218af42..23b2bb4cbd 100644
--- a/lib/open_project/authentication/strategies/warden/doorkeeper_oauth.rb
+++ b/lib/open_project/authentication/strategies/warden/doorkeeper_oauth.rb
@@ -31,7 +31,7 @@ module OpenProject
             if client_credential_user = find_credential_app_user(token.application_id)
               authenticate_user client_credential_user
             else
-              fail!(I18n.t('oauth.authorization_error_client_credentials'))
+              success! User.anonymous
             end
           end
 
diff --git a/spec/requests/oauth/client_credentials_flow_spec.rb b/spec/requests/oauth/client_credentials_flow_spec.rb
new file mode 100644
index 0000000000..61f3ee980c
--- /dev/null
+++ b/spec/requests/oauth/client_credentials_flow_spec.rb
@@ -0,0 +1,80 @@
+#-- copyright
+# OpenProject is a project management system.
+# Copyright (C) 2012-2018 the OpenProject Foundation (OPF)
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2017 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See docs/COPYRIGHT.rdoc for more details.
+#++
+
+require 'spec_helper'
+require 'rest-client'
+
+describe 'OAuth client credentials flow', type: :request do
+  include Rack::Test::Methods
+
+  let!(:application) { FactoryBot.create(:oauth_application, client_credentials_user_id: user_id, name: 'Cool API app!') }
+  let(:client_secret) { application.plaintext_secret }
+
+  let(:access_token) {
+    response = post '/oauth/token',
+                    grant_type: 'client_credentials',
+                    scope: 'api_v3',
+                    client_id: application.uid,
+                    client_secret: client_secret
+
+    expect(response).to be_successful
+    body = JSON.parse(response.body)
+    body['access_token']
+  }
+
+  subject do
+    # Perform request with it
+    headers = { 'HTTP_CONTENT_TYPE' => 'application/json', 'HTTP_AUTHORIZATION' => "Bearer #{access_token}" }
+    response = get '/api/v3', {}, headers
+    expect(response).to be_successful
+
+    JSON.parse(response.body)
+  end
+
+  before do
+    expect(access_token).to be_present
+    expect(subject).to be_present
+  end
+
+  describe 'when application provides client credentials impersonator' do
+    let(:user) { FactoryBot.create(:user) }
+    let(:user_id) { user.id }
+
+    it 'allows client credential flow as the user' do
+      expect(subject.dig('_links', 'user', 'href')).to eq("/api/v3/users/#{user.id}")
+    end
+  end
+
+  describe 'when application does not provide client credential impersonator' do
+    let(:user_id) { nil }
+
+    it 'allows client credential flow as the anonymous user' do
+      expect(subject.dig('_links', 'user', 'href')).to be_nil
+    end
+  end
+end