I’ve been learning iOS for 5 months with no previous experience in programming language so I’m a newbie. I’m learning how to create a more robust and scalable networking layer in Swift. So far so good i can understand what is going on in here however I’m struggling to refactor my code to accept both POST and GET requests. I have received authorization key for my POST request but I have no idea how to do it. Please give me some guidance

protocol HTTPDataDownloader {
    func fetchData <T: Decodable>(as type: T.Type, endpoint: String) async throws -> T
}

extension HTTPDataDownloader {
    func fetchData <T: Decodable>(as type: T.Type, endpoint: String) async throws -> T {
        guard let url = URL(string: endpoint) else {
            throw APIError.requestFailed(description: "Invalid URL")
        }
        let (data, response) = try await URLSession.shared.data(from: url)
        
        guard let httpResponse = response as? HTTPURLResponse else {
            throw APIError.requestFailed(description: "Request failed")
        }
        guard httpResponse.statusCode == 200 else {
            throw APIError.invalidStatusCode(statuscode: httpResponse.statusCode)
        }
        do {
            return try JSONDecoder().decode(type, from: data)
        } catch {
            throw error as? APIError ?? .unknownError(error: error)
        }
    }
}

class CommentsDataService: HTTPDataDownloader {
    private let urlString = "https://jsonplaceholder.typicode.com/posts/1/comments"
    
    func fetchComments() async throws -> [Comments] {
        return try await fetchData(as: [Comments].self, endpoint: urlString)
    }
}
    
@Observable
class CommentsViewModel {
    var comments = [Comments]()
    var errorMessage: String?
    
    private let service: CommentsDataService
    
    init(service: CommentsDataService) {
        print("DEBUG: did init")
        self.service = service
        Task { await fetchComments() }
    }
    
    @MainActor
    func fetchComments() async {
        do {
            self.comments = try await service.fetchComments()
        } catch {
            guard let error = error as? APIError else { return }
            self.errorMessage = error.customDescription
        }
    }
}


struct Comments: Codable, Identifiable {
    let id: Int
    let name: String
    let email: String
    let body: String
}

enum APIError: Error {
    case invalidData
    case jsonParsingFailure
    case requestFailed(description: String)
    case invalidStatusCode(statuscode: Int)
    case unknownError(error: Error)
    
    var customDescription: String {
        switch self {
        case .invalidData:
            return "Invalid data"
        case .jsonParsingFailure:
            return "Failed to parse JSON"
        case .requestFailed(let description):
            return "Request failed: (description)"
        case .invalidStatusCode(let statuscode):
            return "Invalid status code (statuscode)"
        case .unknownError(let error):
            return "An unknown error occured (error)"
        }
    }
}