private const int DEFAULT_EXPIRATION = 43200; //12 hours
/// <summary>
/// This method takes the required VAPID parameters and returns the required
/// header to be added to a Web Push Protocol Request.
/// </summary>
/// <param name="audience">This must be the origin of the push service.</param>
/// <param name="subject">This should be a URL or a 'mailto:' email address</param>
/// <param name="publicKey">The VAPID public key as a base64 encoded string</param>
/// <param name="privateKey">The VAPID private key as a base64 encoded string</param>
/// <param name="expiration">The expiration of the VAPID JWT.</param>
/// <returns>Authorization header value.</returns>
public static string GetVapidAuthenticationHeader(string audience, string subject, string publicKey,
string privateKey, DateTime?expiration = null)
{
ValidateAudience(audience);
ValidateSubject(subject);
ValidatePublicKey(publicKey);
ValidatePrivateKey(privateKey);
if (!expiration.HasValue)
{
expiration = DateTime.UtcNow.AddSeconds(DEFAULT_EXPIRATION);
}
else
{
ValidateExpiration(expiration.Value);
}
var decodedPrivateKey = UrlBase64Encoder.Decode(privateKey);
var decodedPublicKey = UrlBase64Encoder.Decode(publicKey);
var privateECDsa = GetECDsaByPrivateKey(decodedPublicKey, decodedPrivateKey);
//Create JWT token and sign it using ECDsa
var securityToken = new JwtSecurityToken(
audience: audience,
claims: new[] { new Claim("sub", subject) },
expires: expiration,
signingCredentials: new SigningCredentials(new ECDsaSecurityKey(privateECDsa), SecurityAlgorithms.EcdsaSha256));
var jwToken = new JwtSecurityTokenHandler().WriteToken(securityToken);
return($"vapid t={jwToken}, k={publicKey}");
}
public static void ValidatePublicKey(string publicKey)
{
if (string.IsNullOrEmpty(publicKey))
{
throw new ArgumentException("Valid public key not set.");
}
var decodedPublicKey = UrlBase64Encoder.Decode(publicKey);
if (decodedPublicKey.Length != 65)
{
throw new ArgumentException("Vapid public key must be 65 characters long when decoded.");
}
}
public static void ValidatePrivateKey(string privateKey)
{
if (string.IsNullOrEmpty(privateKey))
{
throw new ArgumentException("Valid private key not set.");
}
var decodedPrivateKey = UrlBase64Encoder.Decode(privateKey);
if (decodedPrivateKey.Length != 32)
{
throw new ArgumentException("Vapid private key should be 32 bytes long when decoded.");
}
}