`URLProtocol` sample code

UserProtocol.swift

struct User: Encodable {
    let firstName: String
    let lastName: String
    let admin: Bool
}

final class UserProtocol: URLProtocol {
    
    override class func canInit(with request: URLRequest) -> Bool {
        return true // Customize here
    }
    
    override class func canonicalRequest(for request: URLRequest) -> URLRequest {
        return request // Customize here
    }
    
    override func startLoading() {
        guard let client = client else { return }
        
        let headerFields: [String: String] = [
            "Content-Type": "application/json"
        ]
        
        if let response = HTTPURLResponse(url: url, statusCode: 200, httpVersion: "1.1", headerFields: headerFields) {
            client.urlProtocol(self, didReceive: response, cacheStoragePolicy: .notAllowed)
        }
        
        let user = User(firstName: "John", lastName: "Doe", admin: true)
        guard let data = try? JSONEncoder().encode(user) else { return }
        client.urlProtocol(self, didLoad: data)
        client.urlProtocolDidFinishLoading(self)
    }
    
    override func stopLoading() { }
}

// Configure your URL session here
let urlconfig = URLSessionConfiguration.default
urlconfig.protocolClasses = [UserProtocol.self]

let session = URLSession(configuration: urlconfig)

Thank you