Move expiry period to options

Move the configured lifetime for generated client secrets to the options class.

src/AspNet.Security.OAuth.Apple/AppleAuthenticationOptions.cs

@@ -32,6 +32,15 @@ public AppleAuthenticationOptions()
             Scope.Add("email");
         }
 
+        /// <summary>
+        /// Gets or sets the period of time after which generated client secrets expire
+        /// if <see cref="GenerateClientSecret"/> is set to <see langword="true"/>.
+        /// </summary>
+        /// <remarks>
+        /// The default client secret lifetime is six months.
+        /// </remarks>
+        public TimeSpan ClientSecretExpiresAfter { get; set; } = TimeSpan.FromSeconds(15777000); // 6 months in seconds
+
         /// <summary>
         /// Gets or sets the <see cref="AppleAuthenticationEvents"/> used to handle authentication events.
         /// </summary>

src/AspNet.Security.OAuth.Apple/AppleClientSecretGenerator.cs

@@ -4,7 +4,6 @@
  * for more information concerning the license and the contributors participating to this project.
  */
 
-using System;
 using System.Threading.Tasks;
 
 namespace AspNet.Security.OAuth.Apple
@@ -14,14 +13,6 @@ namespace AspNet.Security.OAuth.Apple
     /// </summary>
     public abstract class AppleClientSecretGenerator
     {
-        /// <summary>
-        /// Gets or sets the period of time after which generated client secrets expire.
-        /// </summary>
-        /// <remarks>
-        /// The default client secret lifetime is six months.
-        /// </remarks>
-        public TimeSpan ExpiresAfter { get; set; } = TimeSpan.FromSeconds(15777000); // 6 months in seconds
-
         /// <summary>
         /// Generates a client secret for Sign In with Apple as an asynchronous operation.
         /// </summary>

src/AspNet.Security.OAuth.Apple/Internal/DefaultAppleClientSecretGenerator.cs

@@ -60,7 +60,7 @@ public override async Task<string> GenerateAsync([NotNull] AppleGenerateClientSe
         private async Task<(string clientSecret, DateTimeOffset expiresAt)> GenerateNewSecretAsync(
             [NotNull] AppleGenerateClientSecretContext context)
         {
-            var expiresAt = _clock.UtcNow.Add(ExpiresAfter).UtcDateTime;
+            var expiresAt = _clock.UtcNow.Add(context.Options.ClientSecretExpiresAfter).UtcDateTime;
             var subject = new Claim("sub", context.Options.ClientId);
 
             _logger.LogDebug(