/// <summary>
/// Generates key authorization string.
/// </summary>
/// <param name="key">The key.</param>
/// <param name="token">The challenge token.</param>
/// <returns></returns>
public static string KeyAuthorization(this IAccountKey key, string token) => $"{token}.{key.Thumbprint()}";
/// <summary>
/// Computes the key authorization string for <paramref name="challenge"/>.
/// </summary>
/// <param name="challenge">The challenge.</param>
/// <param name="key">The key.</param>
/// <returns>The key authorization string.</returns>
public static string ComputeKeyAuthorization(this ChallengeEntity challenge, IAccountKey key)
=> $"{challenge.Token}.{key.Thumbprint()}";
