OAuth login

auth.swift

import Foundation
import Combine

class OAuthLogin {

    static let shared = OAuthLogin()

    let baseURL = "https://your-auth-server.com"
    let clientID = "your-client-id"
    let clientSecret = "your-client-secret"
    let scope = "your-scope"

    var accessToken: String?
    var refreshToken: String?

    private var cancellable: AnyCancellable?

    private init() {}

    func login(username: String, password: String) -> AnyPublisher<Void, Error> {

        let parameters = [
            "grant_type": "password",
            "username": username,
            "password": password,
            "scope": scope
        ]

        let headers = ["Authorization": "Basic \(base64EncodedCredentials())"]

        let url = URL(string: "\(baseURL)/oauth/token")!

        var request = URLRequest(url: url)
        request.httpMethod = "POST"
        request.allHTTPHeaderFields = headers
        request.httpBody = parameters.percentEncoded()

        return URLSession.shared.dataTaskPublisher(for: request)
            .map(\.data)
            .decode(type: TokenResponse.self, decoder: JSONDecoder())
            .handleEvents(receiveOutput: { [weak self] tokenResponse in
                self?.accessToken = tokenResponse.accessToken
                self?.refreshToken = tokenResponse.refreshToken
            })
            .map { _ in }
            .catch { error -> Empty<Void, Error> in
                return Empty(completeImmediately: true)
            }
            .eraseToAnyPublisher()
    }

    private func base64EncodedCredentials() -> String {
        let credentialsData = "\(clientID):\(clientSecret)".data(using: .utf8)!
        let base64Credentials = credentialsData.base64EncodedString()
        return base64Credentials
    }
}

struct TokenResponse: Codable {
    let accessToken: String
    let refreshToken: String
    let expiresIn: Int

    private enum CodingKeys: String, CodingKey {
        case accessToken = "access_token"
        case refreshToken = "refresh_token"
        case expiresIn = "expires_in"
    }
}

extension Dictionary {
    func percentEncoded() -> Data? {
        return map { key, value in
            let escapedKey = "\(key)".addingPercentEncoding(withAllowedCharacters: .urlQueryValueAllowed) ?? ""
            let escapedValue = "\(value)".addingPercentEncoding(withAllowedCharacters: .urlQueryValueAllowed) ?? ""
            return escapedKey + "=" + escapedValue
        }
        .joined(separator: "&")
        .data(using: .utf8)
    }
}

extension CharacterSet {
    static let urlQueryValueAllowed: CharacterSet = {
        var allowed = CharacterSet.urlQueryAllowed
        allowed.remove(charactersIn: "&=")
        return allowed
    }()
}