Feature request: add support for audience claim in role config

[rdt12]

Hi Dave,

This was discussed in #ligo-scitokens on the OSG slack. I'm adding it here so it isn't forgotten.

I think it would be very useful to be able to restrict the audience as well as the scope when defining a role. It seems like this could be implemented by setting token_url_params in the role config.

Thanks, Ron

[DrDaveD]

I'm not convinced that a role should define an audience. Audiences are intended to distinguish between different servers for very similar services, and roles probably should be associated with a service. I think that if it's actually a different service that you're trying to distinguish between that it makes more sense to associate that with different scopes, and roles already map to scopes.