Many modern RESTful web service APIs are implementing JSON Web Tokens
for authentication, which significantly streamlines and enhances the HTTP authentication process. Named Credentials can store the endpoint, username, and password for external web services, but they do not currently have a facility for storing the JWT returned by the service after the login call. These JWTs can often have an extended shelf life (i.e. days or weeks), so it would be useful to be able to store them under the Named Credential, retrieve them when needed, and refresh them when they expire. This would dramatically reduce the amount of custom Apex code required to build and maintain integrations to these endpoints.