ios_jwt.swift

import UIKit
import CryptoKit


func jwt(header: String, payload: String, secret: String) -> String {
	func base64URLencode(_ s: String) -> String {
		return s.replacingOccurrences(of: "/", with: "_").replacingOccurrences(of: "+", with: "-")
	}

	let headerData = base64URLencode(header).data(using: .utf8)!.base64EncodedString()
	let payloadData = base64URLencode(payload).data(using: .utf8)!.base64EncodedString()

	let body = headerData + "." + payloadData

	var hmac = HMAC<SHA256>(key: SymmetricKey(data: secret.data(using: String.Encoding.utf8)!))
	hmac.update(data: body.data(using: .utf8)!)
	let signature = base64URLencode(Data(hmac.finalize()).base64EncodedString())
	return headerData + "." + payloadData + "." + signature
}