1 files changed, 57 insertions, 0 deletions
diff --git a/app/controllers/jira_connect/application_controller.rb b/app/controllers/jira_connect/application_controller.rb
new file mode 100644
index 00000000000..a84f25998a6
--- /dev/null
+++ b/app/controllers/jira_connect/application_controller.rb
@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+class JiraConnect::ApplicationController < ApplicationController
+  include Gitlab::Utils::StrongMemoize
+
+  skip_before_action :authenticate_user!
+  skip_before_action :verify_authenticity_token
+  before_action :verify_atlassian_jwt!
+
+  attr_reader :current_jira_installation
+
+  private
+
+  def verify_atlassian_jwt!
+    return render_403 unless atlassian_jwt_valid?
+
+    @current_jira_installation = installation_from_jwt
+  end
+
+  def verify_qsh_claim!
+    payload, _ = decode_auth_token!
+
+    # Make sure `qsh` claim matches the current request
+    render_403 unless payload['qsh'] == Atlassian::Jwt.create_query_string_hash(request.url, request.method, jira_connect_base_url)
+  rescue
+    render_403
+  end
+
+  def atlassian_jwt_valid?
+    return false unless installation_from_jwt
+
+    # Verify JWT signature with our stored `shared_secret`
+    decode_auth_token!
+  rescue JWT::DecodeError
+    false
+  end
+
+  def installation_from_jwt
+    return unless auth_token
+
+    strong_memoize(:installation_from_jwt) do
+      # Decode without verification to get `client_key` in `iss`
+      payload, _ = Atlassian::Jwt.decode(auth_token, nil, false)
+      JiraConnectInstallation.find_by_client_key(payload['iss'])
+    end
+  end
+
+  def decode_auth_token!
+    Atlassian::Jwt.decode(auth_token, installation_from_jwt.shared_secret)
+  end
+
+  def auth_token
+    strong_memoize(:auth_token) do
+      params[:jwt] || request.headers['Authorization']&.split(' ', 2)&.last
+    end
+  end
+end