struct User : Content, PostgreSQLModel, Parameters {

var id : Int?
private(set) var email: String
private(set) var password: String

}

extension User: BasicAuthenticatable {

static let usernameKey: WritableKeyPath<User, String> = .email
static let passwordKey: WritableKeyPath<User, String> = .password

}

private extension UserController {

func registerUser(_ request: Request, newUser: User) throws -> Future<HTTPResponseStatus> {

    return try User.query(on: request).filter(.email == newUser.email).first().flatMap { existingUser in

    guard existingUser == nil else {
            throw Abort(.badRequest, reason: "a user with this email already exists" , identifier: nil)
        }

        let digest = try request.make(BCryptDigest.self)
        let hashedPassword = try digest.hash(newUser.password)
        let persistedUser = User(id: nil, email: newUser.email, password: hashedPassword)

    return persistedUser.save(on: request).transform(to: .created)
  }
 }
}