JWT Swift5 + Common Crypto

jwt.swift

import Foundation
import CommonCrypto

public func jwt(payload: [String: Any], secret: String) -> String? {
    guard let data = try? JSONSerialization.data(withJSONObject: payload, options: []) else {
        return nil
    }
    return jwt(payload: data, secret: secret)
}

public func jwt(payload: Data, secret: String) -> String? {
    guard let str = String(data: payload, encoding: .utf8) else {
        return nil
    }
    return jwt(payload: str, secret: secret)
}

public func jwt<T: Encodable>(payload: T, secret: String) -> String? {
    guard let data = try? JSONEncoder().encode(payload) else {
        return nil
    }
    return jwt(payload: data, secret: secret)
}

public func jwt(payload: String, secret: String) -> String? {
    
    guard let payload64String = payload.data(using: .utf8)?.base64EncodedString() else {
        return nil
    }
    
    let headers = """
    {"alg":"HS256","typ":"JWT"}
    """
    
    guard let headers64String = headers.data(using: .utf8)?.base64EncodedString() else {
        return nil
    }
    
    var jwt = "\(headers64String).\(payload64String)"
    guard let signature = jwt.hmac256(secret: secret) else {
        return nil
    }
    jwt += ".\(signature)"
    
    return jwt
}

private extension String {
    
    func hmac256(secret: String) -> String? {
        guard let dataCharPtr = self.base64URL.cString(using: .utf8) else { return nil }
        guard let keyCharPtr = secret.cString(using: .utf8) else { return nil }
        var digest = [UInt8](repeating: 0, count: Int(CC_SHA256_DIGEST_LENGTH))
        CCHmac(
            CCHmacAlgorithm(kCCHmacAlgSHA256),
            keyCharPtr,
            strlen(keyCharPtr),
            dataCharPtr,
            strlen(dataCharPtr),
            &digest
        )
        return Data(digest).base64EncodedString().base64URL
    }
    
    /// https://en.wikipedia.org/wiki/Base64#Variants_summary_table
    var base64URL: String {
        return self
        .replacingOccurrences(of: "=", with: "")
        .replacingOccurrences(of: "+", with: "-")
        .replacingOccurrences(of: "/", with: "_")
    }

}