Set additional property to URLRequest

URLRequest+Property.swift

extension URLRequest {

    func property(forKey key: String) -> Any? {
        return URLProtocol.property(forKey: key, in: self)
    }

    mutating func setProperty(_ value: Any, forKey key: String) {
        mutate { URLProtocol.setProperty(value, forKey: key, in: $0) }
    }

    mutating func removeProperty(forKey key: String) {
        mutate { URLProtocol.removeProperty(forKey: key, in: $0) }
    }

    private mutating func mutate(_ block: (NSMutableURLRequest) -> Void) {
        let mutableURLRequest = self as! NSMutableURLRequest
        block(mutableURLRequest)
        self = mutableURLRequest as URLRequest
    }
}