Caps-Server/Sources/App/Authenticator.swift

import Foundation
import Vapor

final class Authenticator {

    private var writers: Set<String>

    init(writers: [String]) {
        self.writers = Set(writers)
    }

    func hasAuthorization(for key: String) -> Bool {
        // Note: This is not a constant-time compare, so there may be an opportunity
        // for timing attack here. Sets perform hashed lookups, so this may be less of an issue,
        // and we're not doing anything critical in this application.
        // Worst case, an unauthorized person with a lot of free time and energy to hack this system
        // is able to change contents of the database, which are backed up in any case.
        writers.contains(key)
    }

    func authorize(_ request: Request) throws {
        guard let key = request.headers.first(name: "key") else {
            throw Abort(.badRequest) // 400
        }
        guard hasAuthorization(for: key) else {
            throw Abort(.forbidden) // 403
        }
    }
}