val requestingUserAttribute = AttributeKey<User>("requestingUser")

/**
 * Intercepts the call pipeline after the auth stage and attaches a user to the incoming
 * call.
 */
fun Route.addUserAttributeInterceptor(userService: UserService) {
    // Typically we'd intercept the feature phase but in this case we want to intercept
    // after the authentication feature runs, which happens right before the call phase
    intercept(ApplicationCallPipeline.Call) {
        val principal = call.principal<JWTPrincipal>() ?: throw DataReferenceError("No claim found")
        val userID = principal.payload.getClaim(USER_ID_CLAIM_NAME).asInt() ?:
            throw DataReferenceError("Principal does not have user ID")
		// DataReferenceError is a custom error in my code that gets caught by status pages
        val user = userService.getUser(userID) ?: throw DataReferenceError("Could not find user $userID from claim.")
		// Now any routing block that calls addUserAttributeInterceptor can retrieve calling user from call.attributes[requestingUserAttribute]
        call.attributes.put(requestingUserAttribute, user)
    }
}