Allow user to set keyvault secret client option

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureAppConfigurationKeyVaultOptions.cs

@@ -15,6 +15,7 @@ namespace Microsoft.Extensions.Configuration.AzureAppConfiguration
     public class AzureAppConfigurationKeyVaultOptions
     {
         internal TokenCredential Credential;
+        internal SecretClientOptions ClientOptions = new SecretClientOptions();
         internal List<SecretClient> SecretClients = new List<SecretClient>();
         internal Func<Uri, ValueTask<string>> SecretResolver;
         internal Dictionary<string, TimeSpan> SecretRefreshIntervals = new Dictionary<string, TimeSpan>();
@@ -31,6 +32,17 @@ public AzureAppConfigurationKeyVaultOptions SetCredential(TokenCredential creden
             return this;
         }
 
+        /// <summary>
+        /// Configures the client options used when connecting to key vaults that have no registered <see cref="SecretClient"/>. 
+        /// The client options will not affect <see cref="SecretClient"/> instances registered via <see cref="Register(SecretClient)"/>.
+        /// </summary>
+        /// <param name="configure">A callback used to configure secret client options.</param>
+        public AzureAppConfigurationKeyVaultOptions ConfigureClientOptions(Action<SecretClientOptions> configure)
+        {
+            configure?.Invoke(ClientOptions);
+            return this;
+        }
+
         /// <summary>
         /// Registers the specified <see cref="SecretClient"/> instance to use to resolve key vault references for secrets from associated key vault.
         /// </summary>

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureKeyVaultReference/AzureKeyVaultSecretProvider.cs

@@ -115,8 +115,13 @@ private SecretClient GetSecretClient(Uri secretUri)
                 return null;
             }
 
-            client = new SecretClient(new Uri(secretUri.GetLeftPart(UriPartial.Authority)), _keyVaultOptions.Credential);
+            client = new SecretClient(
+                new Uri(secretUri.GetLeftPart(UriPartial.Authority)),
+                _keyVaultOptions.Credential,
+                _keyVaultOptions.ClientOptions);
+
             _secretClients.Add(keyVaultId, client);
+
             return client;
         }