Configure the Conga Composer Connected App
Administrators can pre-approve users to connect via OAuth when running Composer solutions. This method masks the session ID and URL when using Visualforce buttons, and prevents authorization requests when using Composer OAuth buttons, and prevents pop-up authorization requests on mobile devices when running Composer solutions on Salesforce Mobile.
In addition to configuring Conga Composer as a Connected App, create Conga Composer OAuth buttons (or update existing non-OAuth buttons) to launch your Composer solutions. This is not required in Salesforce Classic, but it is required in Salesforce Lightning.