Is your feature request related to a problem? Please describe.

Currently there is no easy way to specify a gem's metadata. Metadata is often used to reference related links for a given gem, but is otherwise a generic key/value dictionary that can be looked up by consumers of the gem. For example, can be used to specify if multi factor authentication is required when publishing on rubygems (rails example).

Describe the solution you'd like

Add support for specifying the gem's metadata through an additional property in the same way it's already possible to specify the likes of summary, author, homepage, ...

Describe alternatives you've considered

My current work around is to apply some sed magic as a postprocessing step to the final gemspec file but that's very brittle.

Additional context

This is not just useful, but actually necessary in some cases. For example, gems published to the internal github package repository must specify a github_repo attribute in the metadata (docs), similar if mfa needs to be enforced before publishing to rubygems (see rails example above).