Rails 5 API Key Pair Design Pattern

How do I make my Rails 5 API-only work with key pairs pattern? I can't consider JWT because of these requirements

I want to:

• Keep track of the apps using the API
• Securely verify the resources ownership without username/password.

I could think of this process:

• User create new app in our webapp.
• The system generates a secured public key (the app identifier) and a private key
• User can use the key-pair to integrate the API with their apps in different languages as long as they can submit the HTTP request.
• The server will verify their key-pair and respond accordingly.

My questions:

• Is there any gem to handle key-pair generating? (just for references)
• I would prefer to generate the key-pair myself rather than using a gem. What algorithm best suits my requirements?
• Should I expire the key-pair?