What is the fastest/easiest way - step by step, from the beginning - to “code sign” my Qt app on OS X so that it can be distributed?

Question

I am writing a cross-platform app in Qt (using Qt Creator). One of the target platforms is OS X.

The application is being packaged for installation on OS X by using

Answer 1

First of all, please, check the following link

As you wrote, you may distribute your application outside of the App Store. Such bundles or pkg installers should be signed with the Developer ID signing identity. This is the only signature that will pass checks by MacOS GateKeeper.

You must be a "Team Agent" to obtain this. If you are working alone this should be no problem for you. If you are not "Team Agent" you will need to create the certificate request and send it to your "Team Agent" who will generate the public key for you and send it back.

Once you will have a valid Developer ID signing identity (as people wrote in comments) you can just sign your app with similar command line command: codesign "Developer ID ...." myApplicationPath.app

P.S. Latest xCode provides a nice UI to obtain different types of signing identities. Just check the link at the top of answer.