Add support for reading permissions from JSON web tokens issued by Auth0 in Ktor

ktor-auth0-permissions is a very small and slightly opinionated library for dealing with authorization and permissions management. The core features are

• provide an easy way of setting up auhtorization config with JSON web tokens from Auth0
• allow or reject users access to certain endpoints based on if they have certain permissions or not

Permissions are also referred to as "scopes" when they are attached to an M2M (machine-to-machine) token.

The following example install JWT authentication with the "Authentication" future provided by Ktor. Additionally, endpoint /users requires the permission read-users.

private const val AUTHENTICATION_NAMESPACE = "my-application"

fun main() {
    embeddedServer(Netty, 80) {
        // Install JWT authentication, with Auth0
        install(Authentication) {
            auth0(AUTHENTICATION_NAMESPACE)
        }
        routing {
            authenticate(AUTHENTICATION_NAMESPACE) {
                get("/users") {
                    // Require that permission "read-users" is present
                    permission("read-users") {
                        call.respond(HttpStatusCode.OK)
                    }
                }
            }
        }
    }.start(wait = true)
}

It the user has the permission read-users present in their token, they will be granted access to this endpoint and everything in the permission block will be executed. If a token was presented but the permission was missing, status code 403 will be returned.

The following properties must be configured, either as an environment variable or set in a configuration file for the application.